AAPT2: add flag for strict visibility

Will only detect whether a resource was defined as both 'public' and
'private' (but will allow overriding 'undefined' visiblity for now).

Test: TableMerger_test + manual
Bug: 72735798

Change-Id: If0749559c91c4d8820a6286fc9ddc80209c1e5e9
4 files changed