This change adds keybinding support for:
- `Ctrl+B`: Moves the cursor backward one character.
- `Ctrl+F`: Moves the cursor forward one character.
- `Alt+Left Arrow`: Moves the cursor backward one word.
- `Alt+Right Arrow`: Moves the cursor forward one word.
Closes b/411469305.
New keybindings in the main input prompt (when auto-suggestions are not active):
- `Ctrl+L`: Clears the entire screen.
- `Ctrl+A`: Moves the cursor to the beginning of the current input line.
- `Ctrl+E`: Moves the cursor to the end of the current input line.
- `Ctrl+P`: Navigates to the previous command in the input history.
- `Ctrl+N`: Navigates to the next command in the input history.
In the multiline text editor (e.g., when editing a previous message):
- `Ctrl+K`: Deletes text from the current cursor position to the end of the line ("kill line right").