assets should be kept on CPU by default (#11212)

# Objective

- Since #10520, assets are unloaded from RAM by default. This breaks a
number of scenario:
  - using `load_folder`
- loading a gltf, then going through its mesh to transform them /
compute a collider / ...
- any assets/subassets scenario should be `Keep` as you can't know what
the user will do with the assets
  - android suspension, where GPU memory is unloaded

- Alternative to #11202 

## Solution

- Keep assets on CPU memory by default

crates/bevy_gltf/src/loader.rs

@@ -390,7 +390,7 @@ async fn load_gltf<'a, 'b, 'c>(
             let primitive_label = primitive_label(&gltf_mesh, &primitive);
             let primitive_topology = get_primitive_topology(primitive.mode())?;
 
-            let mut mesh = Mesh::new(primitive_topology, RenderAssetPersistencePolicy::Unload);
+            let mut mesh = Mesh::new(primitive_topology, RenderAssetPersistencePolicy::Keep);
 
             // Read vertex attributes
             for (semantic, accessor) in primitive.attributes() {
@@ -434,7 +434,7 @@ async fn load_gltf<'a, 'b, 'c>(
                     let morph_target_image = MorphTargetImage::new(
                         morph_target_reader.map(PrimitiveMorphAttributesIter),
                         mesh.count_vertices(),
-                        RenderAssetPersistencePolicy::Unload,
+                        RenderAssetPersistencePolicy::Keep,
                     )?;
                     let handle =
                         load_context.add_labeled_asset(morph_targets_label, morph_target_image.0);
@@ -726,7 +726,7 @@ async fn load_image<'a, 'b>(
                 supported_compressed_formats,
                 is_srgb,
                 ImageSampler::Descriptor(sampler_descriptor),
-                RenderAssetPersistencePolicy::Unload,
+                RenderAssetPersistencePolicy::Keep,
             )?;
             Ok(ImageOrPath::Image {
                 image,
@@ -748,7 +748,7 @@ async fn load_image<'a, 'b>(
                         supported_compressed_formats,
                         is_srgb,
                         ImageSampler::Descriptor(sampler_descriptor),
-                        RenderAssetPersistencePolicy::Unload,
+                        RenderAssetPersistencePolicy::Keep,
                     )?,
                     label: texture_label(&gltf_texture),
                 })

crates/bevy_render/src/mesh/shape/capsule.rs

@@ -369,7 +369,7 @@ impl From<Capsule> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, vs)
         .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, vns)

crates/bevy_render/src/mesh/shape/cylinder.rs

@@ -123,7 +123,7 @@ impl From<Cylinder> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_indices(Some(Indices::U32(indices)))
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)

crates/bevy_render/src/mesh/shape/icosphere.rs

@@ -108,7 +108,7 @@ impl TryFrom<Icosphere> for Mesh {
 
         Ok(Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_indices(Some(indices))
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, points)

crates/bevy_render/src/mesh/shape/mod.rs

@@ -124,7 +124,7 @@ impl From<Box> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)
         .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)
@@ -179,7 +179,7 @@ impl From<Quad> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_indices(Some(indices))
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)
@@ -263,7 +263,7 @@ impl From<Plane> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_indices(Some(Indices::U32(indices)))
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)

crates/bevy_render/src/mesh/shape/regular_polygon.rs

@@ -60,7 +60,7 @@ impl From<RegularPolygon> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)
         .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)

crates/bevy_render/src/mesh/shape/torus.rs

@@ -89,7 +89,7 @@ impl From<Torus> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_indices(Some(Indices::U32(indices)))
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)

crates/bevy_render/src/mesh/shape/uvsphere.rs

@@ -85,7 +85,7 @@ impl From<UVSphere> for Mesh {
 
         Mesh::new(
             PrimitiveTopology::TriangleList,
-            RenderAssetPersistencePolicy::Unload,
+            RenderAssetPersistencePolicy::Keep,
         )
         .with_indices(Some(Indices::U32(indices)))
         .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, vertices)

crates/bevy_render/src/render_asset.rs

@@ -55,8 +55,8 @@ pub trait RenderAsset: Asset + Clone {
 /// or only need very infrequent access, then set this to Unload. Otherwise, set this to Keep.
 #[derive(Reflect, Serialize, Deserialize, Clone, Copy, PartialEq, Eq, Default, Debug)]
 pub enum RenderAssetPersistencePolicy {
-    #[default]
     Unload,
+    #[default]
     Keep,
 }
 

crates/bevy_render/src/texture/image.rs

@@ -467,7 +467,7 @@ impl Default for Image {
             },
             sampler: ImageSampler::Default,
             texture_view_descriptor: None,
-            cpu_persistent_access: RenderAssetPersistencePolicy::Unload,
+            cpu_persistent_access: RenderAssetPersistencePolicy::Keep,
         }
     }
 }

crates/bevy_render/src/texture/image_loader.rs

@@ -67,7 +67,7 @@ impl Default for ImageLoaderSettings {
             format: ImageFormatSetting::default(),
             is_srgb: true,
             sampler: ImageSampler::Default,
-            cpu_persistent_access: RenderAssetPersistencePolicy::Unload,
+            cpu_persistent_access: RenderAssetPersistencePolicy::Keep,
         }
     }
 }

crates/bevy_sprite/src/texture_atlas_builder.rs

@@ -209,7 +209,7 @@ impl TextureAtlasBuilder {
                             self.format.pixel_size() * (current_width * current_height) as usize
                         ],
                         self.format,
-                        RenderAssetPersistencePolicy::Unload,
+                        RenderAssetPersistencePolicy::Keep,
                     );
                     Some(rect_placements)
                 }