AAPT2: Allow truncating of package names

ResTable_package header only allows 127 UTF-16 characters, so AAPT
would truncate the real package name to fit. AAPT2 would error-out
on any package name longer than 127 UTF-16 characters. This strictness
is not required except when building shared libraries, which use the
full package name as a way of identifying the runtime assigned
package ID to package name mapping.

Bug: 36940145
Test: make aapt2_tests
Change-Id: I7d2b7e50c7ab30c6a6c4f15d310e711f68e35091