Make LoadContext use the builder pattern for loading dependent assets (#13465)
# Objective
- Fixes #13445.
## Solution
- Removes all `load_` methods from `LoadContext`.
- Introduces `fn loader()` which returns a builder.
## Testing
- I've tested with `cargo test --package=bevy_asset` and run the two
relevant examples (`asset_processing` & `asset_decompression`).
---
## Changelog
- Replaced all `load_` methods on `LoadContext` with the new `loader()`
pattern.
## Migration Guide
- Several LoadContext method calls will need to be updated:
- `load_context.load_with_settings(path, settings)` =>
`load_context.loader().with_settings(settings).load(path)`
- `load_context.load_untyped(path)` =>
`load_context.loader().untyped().load(path)`
- `load_context.load_direct(path)` =>
`load_context.loader().direct().load(path)`
- `load_context.load_direct_untyped(path)` =>
`load_context.loader().direct().untyped().load(path)`
- `load_context.load_direct_with_settings(path, settings)` =>
`load_context.loader().with_settings(settings).direct().load(path)`
- `load_context.load_direct_with_reader(reader, path)` =>
`load_context.loader().direct().with_reader(reader).load(path)`
- `load_context.load_direct_with_reader_and_settings(reader, path,
settings)` =>
`load_context.loader().with_settings(settings).direct().with_reader(reader).load(path)`
- `load_context.load_direct_untyped_with_reader(reader, path)` =>
`load_context.loader().direct().with_reader(reader).untyped().load(path)`
---
CC @alice-i-cecile / @bushrat011899
Examples:
```rust
load_context.loader()
.with_asset_type::<A>()
.with_asset_type_id(TypeId::of::<A>())
.with_settings(|mut settings| { settings.key = value; })
// Then, for a Handle<A>:
.load::<A>()
// Or, for a Handle<LoadedUntypedAsset>:
.untyped()
.load()
// Or, to load an `A` directly:
.direct()
.load::<A>()
.await
// Or, to load an `ErasedLoadedAsset` directly:
.direct()
.untyped()
.load()
.await
```
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