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.toml

@@ -49,6 +49,7 @@ sha2 = "0.10"
 fontdb = "0.23"
 ttf-parser = "0.25"
 cosmic-text = "0.15"
+unicode-bidi = "0.3"
 lyon_tessellation = "1.0.20"
 
 [dev-dependencies]