Implemented optional commit-text support with batching.

Key points:
1. New user-setting  
   • Preference key `checkbox_enable_commit_text` with default false added in `PreferenceConfiguration`.  
   • Field `enableCommitText` exposed and populated when preferences are read.

2. StreamView enhancements  
   • `setCommitTextEnabled(boolean)` toggles feature.  
   • When enabled, the view now reports itself as a text-editor and provides a `BaseInputConnection`.  
   • Added callbacks `handleCommitText` / `handleDeleteSurroundingText` to `InputCallbacks` and invoke them from the custom `InputConnection`.

3. Game activity  
   • Registers the new preference (`prefConfig.enableCommitText`) via `streamView.setCommitTextEnabled(...)`.  
   • Implements the two new callback methods.  
   • Adds a queue + handler that splits committed text into 512-byte UTF-8 chunks and sends them with 15 ms spacing.  
   • Implements deletion handling by emitting Backspace key events.  

4. Support code  
   • Added constants, imports, and helper fields (Handler, Queue, StandardCharsets, etc.).

All changes are strictly additive and guarded by the new preference, so existing behaviour remains unchanged until the option is enabled.