TextPipeline::update_buffer collect Attrs directly

[ickshonpe]

Objective

We don't need to collect the text components into TextPipeline's spans buffer, and then map them to Cosmic Text Attrs later. Instead we can create and collect the Attrs directly.

Solution

• Store the cosmic text Attrs in TextPipeline::spans_buffer, instead of mapping the collected text components from the spans buffer afterwards.

• Rename spans_buffer to sections_buffer. "Span" is potentially misleading as the root Text/Text2d's text and attributes are also collected into this buffer, not just the TextSpans.

• Remove the FontFaceInfo type, as it is no longer used.

Testing

yellow = this PR, red = main 7a436e3

cargo run --example many_buttons --release --features="trace_tracy","debug" -- --text --recompute-text

cargo run --example many_text2d --release --features="trace_tracy","debug" -- --recompute