fix(mtext): support arabic cursive shaping and bidirectional rtl text layout

- Enable fallback font metrics for HarfBuzz shaping in TTF glyph resolver

- Implement Unicode Bidirectional Algorithm (UBA) paragraph base direction detection

- Anchor right-to-left paragraphs to right container boundaries by default

- Reorder line atoms with base direction level to preserve neutral punctuation attachment

- Right-align RTL single-line TEXT and handle editor caret placement on RTL glyphs

Cargo.lock

@@ -52,6 +52,7 @@ dependencies = [
  "serde_json",
  "sha2 0.10.9",
  "ttf-parser",
+ "unicode-bidi",
  "ureq",
  "wasm-bindgen",
  "wasm-bindgen-futures",