Make finalize_res flag aware

This continues down the rabbit hole of using regex to parse the staging
file. Modified finalize_item to be called directly with matches and
return a tuple of strings that go in various places. It is a bit cryptic
but so was the inline regex modification before too. The proper solution
is to parse the xml and handle it.

As it is now it is very brittle
1. "removed_" being a magic constant that the rest of the resource
   frameworks knows how to handle
2. It still doesn't handle proper xml and has strong assumptions about
   how the items are listed
3. There is lots of room for improving the python code :)

It is however the path of least resistant right now to get finalization
moving forward.

Flag: EXEMPTE modifying a script used for finalization
Bug: 390120561
Test: frameworks/base/tools/aapt2/tools/finalize_res.py frameworks/base/core/res/res/values/public-staging.xml frameworks/base/core/res/res/values/public-final.xml
Change-Id: I8e3bda38a5229754fa679a79061527bc246d9e08