Force consume caption bar insets in freeform immersive

Adds top padding to DecorView equal to the caption inset when a freeform
window has FULLSCREEN sysUiVisibility is requested. This is to ensure
that the forced-visible caption doesn't occlude app content when a
freeform app tries to enter immersive mode but remains in freeform.

Bug: 316231589
Test: atest WmTests WMShellUnitTests
Flag: com.android.window.flags.enable_caption_compat_inset_force_consumption

Change-Id: I4a4b20591ef6690dba1eaa16abe5f7310597042b