`Sprite`, `Text`, and `Handle<MeshletMesh>` were types of renderable
entities that the new segregated visible entity system didn't handle, so
they didn't appear.
Because `bevy_text` depends on `bevy_sprite`, and the visibility
computation of text happens in the latter crate, I had to introduce a
new marker component, `SpriteSource`. `SpriteSource` marks entities that
aren't themselves sprites but become sprites during rendering. I added
this component to `Text2dBundle`. Unfortunately, this is technically a
breaking change, although I suspect it won't break anybody in practice
except perhaps editors.
Fixes#12935.
## Changelog
### Changed
* `Text2dBundle` now includes a new marker component, `SpriteSource`.
Bevy uses this internally to optimize visibility calculation.
## Migration Guide
* `Text` now requires a `SpriteSource` marker component in order to
appear. This component has been added to `Text2dBundle`.
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