Reduce reading apk resources in startActivity

The permission callback is usually called from
startActivityUnchecked
 > postStartActivityProcessing
  > Interceptor#onActivityLaunched

This centralizes the resource accesses to window style cache.

Bug: 350394503
Flag: com.android.window.flags.cache_window_style
Test: atest ActivityRecordTests#testReadWindowStyle
Change-Id: Ia70c369af6f86879a2fe54e0f1f345c2a7e76bee