Extract text colors per glyph

[ickshonpe]

Objective

Colors are extracted per text section, transforms per glyph.
This makes it awkward to set colors for individual glyphs as they have to be batched separately.

Solution

• Add color: LinearRgba and translation: Vec2 fields to ExtractedGlyph.
• Move the transform fields from ExtractedGlyph and ExtractedUiItem to ExtractedUiNode.
• Move the rect field from ExtractedUiNode to ExtractedUiItem.

ExtractedUiNodes are smaller by 16 bytes, from 208 to 192 bytes in size.
ExtractedGlyphs are smaller by 8 bytes, from 48 to 40 bytes in size.

Testing

Output from the UI examples should be unchanged, main ones to check are testbed_ui, testbed_full_ui, text_debug, text_wrap_debug and ui_transform.

Not a performance motivated change but this should show a marginal improvement over main, YMMV:

cargo run --example many_glyphs --release -- --no-text2d