fix: RTL cursor jumping, character loss, and stale alignment

[ra3orblade]

Summary

• JS-8716, JS-9183: Save text to store before calling setRtl, so intermediate re-renders from the RTL flag/alignment gRPC calls have the correct text. Previously setRtl ran first, causing re-renders with stale text that led to cursor jumps and first-character deletion when switching between LTR↔RTL.
• JS-9183, JS-6395: Derive the isRtl CSS class from actual text content (U.String.checkRtl(text)) instead of the stored fields.isRtlDetected flag. The flag lags behind text changes, keeping direction: rtl on the element after the user has already switched to LTR text.
• JS-6395: Remove the value && guard in setText so that clearing all text properly resets the RTL state. Previously emptying an RTL block kept isRtlDetected=true, so continued LTR typing started with wrong alignment.
• JS-7255: Already fixed by PR Bugfix/JS-7255: The focus behind the RTL text is moving in a different direction #1898 (merged Jan 16) — issue just needs to be closed.
• Minor: checkRtl regex now skips leading whitespace so " مرحبا" is correctly detected as RTL.

Fixes

• JS-6395 — RTL alignment persists when switching to English
• JS-8716 — Cursor jumping when switching from LTR to RTL
• JS-9183 — Select all Arabic then type English → cursor precedes text
• JS-7255 — Focus behind RTL text (already fixed, needs closure)

Test plan

• Type Arabic text in a block, then delete all and type English — alignment should switch to left
• Type Arabic, select all, type English — cursor should be in correct position, no character loss
• Switch keyboard to Arabic in empty block, type first character — character should not be deleted
• Type several Arabic characters, delete all, verify cursor returns to left side
• Type text starting with spaces followed by Arabic — should be detected as RTL
• Undo/redo after switching between RTL and LTR text

🤖 Generated with Claude Code