Update serialize flag for bevy_ecs (#13740)

# Objective

There were some issues with the `serialize` feature:
- `bevy_app` had a `serialize` feature and a dependency on `serde` even
there is no usage of serde at all inside `bevy_app`
- the `bevy_app/serialize` feature enabled `bevy_ecs/serde`, which is
strange
- `bevy_internal/serialize` did not enable `bevy_app/serialize` so there
was no way of serializing an Entity in bevy 0.14

## Solution

- Remove `serde` and `bevy_app/serialize` 
- Add a `serialize` flag on `bevy_ecs` that enables `serde`
- ` bevy_internal/serialize` now enables `bevy_ecs/serialize`

crates/bevy_app/Cargo.toml

@@ -13,7 +13,6 @@ trace = []
 bevy_debug_stepping = []
 default = ["bevy_reflect"]
 bevy_reflect = ["dep:bevy_reflect", "bevy_ecs/bevy_reflect"]
-serialize = ["bevy_ecs/serde"]
 
 [dependencies]
 # bevy
@@ -24,7 +23,6 @@ bevy_utils = { path = "../bevy_utils", version = "0.14.0-dev" }
 bevy_tasks = { path = "../bevy_tasks", version = "0.14.0-dev" }
 
 # other
-serde = { version = "1.0", features = ["derive"], optional = true }
 downcast-rs = "1.2.0"
 thiserror = "1.0"
 

crates/bevy_ecs/Cargo.toml

@@ -15,6 +15,7 @@ trace = []
 multi_threaded = ["bevy_tasks/multi_threaded", "arrayvec"]
 bevy_debug_stepping = []
 default = ["bevy_reflect"]
+serialize = ["dep:serde"]
 
 [dependencies]
 bevy_ptr = { path = "../bevy_ptr", version = "0.14.0-dev" }

crates/bevy_ecs/src/entity/mod.rs

@@ -38,7 +38,7 @@
 mod map_entities;
 #[cfg(feature = "bevy_reflect")]
 use bevy_reflect::Reflect;
-#[cfg(all(feature = "bevy_reflect", feature = "serde"))]
+#[cfg(all(feature = "bevy_reflect", feature = "serialize"))]
 use bevy_reflect::{ReflectDeserialize, ReflectSerialize};
 pub use map_entities::*;
 
@@ -57,7 +57,7 @@ use crate::{
     },
     storage::{SparseSetIndex, TableId, TableRow},
 };
-#[cfg(feature = "serde")]
+#[cfg(feature = "serialize")]
 use serde::{Deserialize, Serialize};
 use std::{fmt, hash::Hash, mem, num::NonZeroU32, sync::atomic::Ordering};
 
@@ -146,7 +146,7 @@ type IdCursor = isize;
 #[cfg_attr(feature = "bevy_reflect", derive(Reflect))]
 #[cfg_attr(feature = "bevy_reflect", reflect_value(Hash, PartialEq))]
 #[cfg_attr(
-    all(feature = "bevy_reflect", feature = "serde"),
+    all(feature = "bevy_reflect", feature = "serialize"),
     reflect_value(Serialize, Deserialize)
 )]
 // Alignment repr necessary to allow LLVM to better output
@@ -368,7 +368,7 @@ impl From<Entity> for Identifier {
     }
 }
 
-#[cfg(feature = "serde")]
+#[cfg(feature = "serialize")]
 impl Serialize for Entity {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -378,7 +378,7 @@ impl Serialize for Entity {
     }
 }
 
-#[cfg(feature = "serde")]
+#[cfg(feature = "serialize")]
 impl<'de> Deserialize<'de> for Entity {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where

crates/bevy_internal/Cargo.toml

@@ -71,6 +71,7 @@ shader_format_spirv = ["bevy_render/shader_format_spirv"]
 serialize = [
   "bevy_core/serialize",
   "bevy_input/serialize",
+  "bevy_ecs/serialize",
   "bevy_time/serialize",
   "bevy_window/serialize",
   "bevy_winit?/serialize",

crates/bevy_scene/Cargo.toml

@@ -10,7 +10,7 @@ keywords = ["bevy"]
 
 [features]
 default = ["serialize"]
-serialize = ["dep:serde", "uuid/serde", "bevy_app/serialize"]
+serialize = ["dep:serde", "uuid/serde", "bevy_ecs/serialize"]
 
 [dependencies]
 # bevy