Resolve unused_qualifications warnings (#16001)

# Objective

Fixes the following warning when compiling to wasm.

```
warning: unnecessary qualification
   --> crates\bevy_asset\src\io\mod.rs:733:19
    |
733 |         _cx: &mut core::task::Context<'_>,
    |                   ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: requested on the command line with `-W unused-qualifications`
help: remove the unnecessary path segments
    |
733 -         _cx: &mut core::task::Context<'_>,
733 +         _cx: &mut Context<'_>,
    |
```

## Solution

- Removes the qualification.

crates/bevy_asset/src/io/mod.rs

@@ -728,10 +728,7 @@ struct EmptyPathStream;
 impl Stream for EmptyPathStream {
     type Item = PathBuf;
 
-    fn poll_next(
-        self: Pin<&mut Self>,
-        _cx: &mut core::task::Context<'_>,
-    ) -> Poll<Option<Self::Item>> {
+    fn poll_next(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         Poll::Ready(None)
     }
 }

crates/bevy_tasks/src/wasm_task.rs

@@ -3,7 +3,7 @@ use core::{
     future::{Future, IntoFuture},
     panic::{AssertUnwindSafe, UnwindSafe},
     pin::Pin,
-    task::Poll,
+    task::{Context, Poll},
 };
 
 use futures_channel::oneshot;
@@ -53,10 +53,7 @@ impl<T: 'static> Task<T> {
 
 impl<T> Future for Task<T> {
     type Output = T;
-    fn poll(
-        mut self: core::pin::Pin<&mut Self>,
-        cx: &mut core::task::Context<'_>,
-    ) -> std::task::Poll<Self::Output> {
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         match Pin::new(&mut self.0).poll(cx) {
             Poll::Ready(Ok(Ok(value))) => Poll::Ready(value),
             // NOTE: Propagating the panic here sorta has parity with the async_executor behavior.
@@ -76,7 +73,7 @@ struct CatchUnwind<F: UnwindSafe>(#[pin] F);
 
 impl<F: Future + UnwindSafe> Future for CatchUnwind<F> {
     type Output = Result<F::Output, Panic>;
-    fn poll(self: core::pin::Pin<&mut Self>, cx: &mut core::task::Context) -> Poll<Self::Output> {
+    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
         std::panic::catch_unwind(AssertUnwindSafe(|| self.project().0.poll(cx)))?.map(Ok)
     }
 }