[1/n] Move freeform caption dimen to core

The caption height is required to ensure bounds consider caption insets
when app is first launched as modifying this in Shell will be too late.

Flag: com.android.window.flags.exclude_caption_from_app_bounds
Test: m
Bug: 399544381
Change-Id: Id9619d4168de9d16fa345faf6cf09ae4a6bc64a8