AAPT2: Fix quoted text in res/xml assets

AAPT2 aggressively processed xml nodes and regressed from the behavior
of AAPT. This change restores AAPT's processing of xml nodes with
quotations.

Bug: 71805084
Test: Created tests in XmlFlattener_test.cpp and ran the test in the
Android Studio project given in the bug

Change-Id: Idedb4f1002e9fd705ceb5feae35289235b754b02