AAPT2: Do not overlay comments

Always take the original comment of a resource. Resources passed in
through regular file arguments and resources added using the -R and
--auto-add-overlay flags will keep the same comments when overlayed by
another resource.

This will allow R.java files to remain consistent across devices between
product overlays.

Bug: 70641212
Test: aapt2_tests
Change-Id: I4ed1037a8d42f7e77d85e5c2a8ee78051053831a