bevy::text::PositionedGlyph is undocumented, making it difficult to use.

## How can Bevy's documentation be improved?

[`bevy::text::PositionedGlyph`](https://docs.rs/bevy/latest/bevy/text/struct.PositionedGlyph.html) has no documentation at all. This makes it difficult to know how the struct - or its containing struct, [`bevy::text::TextLayoutInfo`](https://docs.rs/bevy/latest/bevy/text/struct.TextLayoutInfo.html) - can be used.

For instance, I specifically need to access the layout information to know where to place an editor caret according to a glyph index that can change arbitrarily. I don't know whether `TextLayoutInfo` is suitable for this purpose, and neither does one of the maintainers; documenting the item in full would make it much simpler to find use-cases for it.