feat: add language switch key

[naveensingh]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

• Added Show language switch key option to enable/disable a new language switch key.
  • Similar to the existing Show emoji key option, this option also directly mutates the keyboard at runtime, which is a bit hacky but good enough for now.
  • Enabling the language switch key automatically disables the emoji key due to a lack of space. I'll add the emoji key as a secondary long-press key on the comma key in another pull request.
• Updated the space bar to show the currently active language with a smaller text size and reduced alpha. Similar to the language switch key (but not the emoji key), long-pressing the spacebar now displays the language switching dialog.
• Improved space bar cursor control logic. Cursor control is now activated immediately on swipe, similar to Gboard and others.

Tests performed

• Test emoji key
• Test language switch key
• Test opening the language selection dialog by long-pressing on the language key or the spacebar
• Test space bar cursor control

Before & after preview

Closes the following issue(s)

• Closes Faster language switching #62
• Partially addresses Improve spacebar cursor control #129

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.