Instead of extracting an individual sprite per glyph of a text spawn or
slice of a nine-patched sprite, add a buffer to store the extracted
slice geometry.
Fixes#16972
* New struct `ExtractedSlice` to hold sprite slice size, position and
atlas info (for text each glyph is a slice).
* New resource `ExtractedSlices` that wraps the `ExtractedSlice` buffer.
This is a separate resource so it can be used without sprites (with a
text material, for example).
* New enum `ExtractedSpriteKind` with variants `Single` and `Slices`.
`Single` represents a single sprite, `Slices` contains a range into the
`ExtractedSlice` buffer.
* Only queue a single `ExtractedSprite` for sets of glyphs or slices and
push the geometry for each individual slice or glyph into the
`ExtractedSlice` buffer.
* Modify `ComputedTextureSlices` to return an `ExtractedSlice` iterator
instead of `ExtractedSprites`.
* Modify `extract_text2d_sprite` to only queue new `ExtractedSprite`s on
font changes and otherwise push slices.
I don't like the name `ExtractedSpriteKind` much, it's a bit redundant
and too haskellish. But although it's exported, it's not something users
will interact with most of the time so don't want to overthink it.
yellow = this pr, red = main
```cargo run --example many_glyphs --release --features "trace_tracy" -- --no-ui```
<img width="454" alt="many-glyphs" src="https://github.com/user-attachments/assets/711b52c9-2d4d-43c7-b154-e81a69c94dce" />
```cargo run --example many_text2d --release --features "trace_tracy"```
<img width="415" alt="many-text2d"
src="https://github.com/user-attachments/assets/5ea2480a-52e0-4cd0-9f12-07405cf6b8fa"
/>
* `ExtractedSprite` has a new `kind: ExtractedSpriteKind` field with
variants `Single` and `Slices`.
- `Single` represents a single sprite. `ExtractedSprite`'s `anchor`,
`rect`, `scaling_mode` and `custom_size` fields have been moved into
`Single`.
- `Slices` contains a range that indexes into a new resource
`ExtractedSlices`. Slices are used to draw elements composed from
multiple sprites such as text or nine-patched borders.
* `ComputedTextureSlices::extract_sprites` has been renamed to
`extract_slices`. Its `transform` and `original_entity` parameters have
been removed.
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Co-authored-by: Kristoffer Søholm <k.soeholm@gmail.com>
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