Refactor letterbox logic in separate classes.

Changes:
- Moves logic related to letterbox UI from ActivityRecord to LetterboxUiController.
- Moves logic related to letterbox config values and their get/set/reset methods from WindowManagerService to LetterboxConfiguration.
- Replace multiple letterbox ADB commands with one.

Fix: 183754168
Test: atest SizeCompatTests and adb shell cmd window get|set|reset-letterbox-style
Change-Id: Ic70c900f4f6571f8ecb7c7d5edc2a24014b766ed