feat: finalize floating keyboard option (#663)

[prince-0408]

Description

This PR finalizes the floating keyboard feature as requested in #663 by updating the float toggle key icon behavior and removing obsolete layout setting options.

Key Changes

1. Dynamic Floating Key Icon:

   • Updated ic_keyboard_dismiss.xml vector drawable to represent a down chevron inside a square frame.
   • Updated KeyboardView.kt so that when KeyboardBase.KEYCODE_FLOAT_TOGGLE is drawn, it dynamically shows:
     • Down chevron in a square (ic_keyboard_dismiss) when the keyboard is currently in floating mode.
     • Move/float icon (ic_float_keyboard) when the keyboard is docked.

2. UI & Preferences Cleanup:

   • Removed obsolete "Floating key on keyboard" layout switch option from LanguageSettingsScreen.kt.
   • Removed obsolete "Clipboard key on keyboard" layout preference options from LanguageSettingsScreen.kt.
   • Cleaned up PreferencesHelper.kt by removing FLOATING_KEY_ON_KEYBOARD and CLIPBOARD_KEY_ON_KEYBOARD constants, setters, and getters.
   • Removed isFloatingKeyEnabled() and isClipboardKeyEnabled() methods from KeyboardContextProvider interface in KeyboardBase.kt and GeneralKeyboardIME.kt.
   • Cleaned up unused string resources in strings.xml.

Related Issue

Closes #663

Verification & Testing

• Automated Gradle build test passed cleanly via ./gradlew assembleDebug.
• Verified string resources and UI layout settings screen compiling without lint errors.

Screenshots

[andrewtavis]

praise: All's really great here, @prince-0408! Really thanks so much for the quick reaction and the clean up here! 😊