Raw attribute values are not included in xml files when building binary
APKs but they are when building proto APKs. Remove raw attribute values
and create a new convert flag that (--keep-raw-values) that allows raw
value to be kept.
Also added flag to link to keep raw attribute values.
Bug: 115915884
Bug: 116700688
Test: aapt2_tests
Change-Id: Id50136b775b3f43d159ca06181282f6a7b8eaf40
