Persist whether xml resources have flags

This stores whether an xml document has feature flags in it in a
ResTable_entry so that at runtime we can know not to do extra work
looking for flags.

Test: Automation
Bug: 377974898
Flag: android.content.res.layout_readwrite_flags

Change-Id: Id43b2d9941d1fab8c654d081bf19df5a33a464f3