Fix bug: AOSP keyboard is shown incompletely in Android V landscape mode

Root cause: The AOSP keyboard uses `DisplayMetrics#widthPixels` to calculate the keyboard width and draw keys. Since Android 15’s edge-to-edge enforcement, this property now returns the full screen width, including window insets. This results in an incorrectly large key width calculation.

Fix: Subtract window insets including system bar and display cutout from the width.

Change-Id: Iea01ba749a48145cf5b484dc22a570874b1b7ca4
Test: use `m LatinIME` to install the AOSP keyboard and test landscape mode manually
Bug: 377594757