Move R.txt and make aapt2 generate it

Move R.txt from $(intermediates.COMMON)/src to $(intermediates.COMMON)
in preparation for moving aapt/aapt2 java files out of src.  Also
make aapt2 generate R.txt, and make it an implicit output of the rule
and and input to the aar rule.

Bug: 73885582
Test: m out/target/common/obj/JAVA_LIBRARIES/SettingsLib_intermediates/javalib.aar
Test: m checkbuild
Change-Id: Ia858de226355965b69794c002f841333df16a612