Convert abi warnings to errors.

Convert abi warnings to errors by removing the -advice-only flag from
the invocation of header-abi-diff. This will only apply to branches with
reference abi dumps checked into prebuilts/abi-dumps/(v)ndk (since
abi-diffing will only be triggered on them.)

Also allow for:

1) Extensions.
2) Changes to types in exported headers, unreferenced by public symbols still
   trigger warnings.
3) Any removal of symbols appearing in a shared library's .dynsym table, but not
   in exported headers is still a warning.

Bug: 64267858

Test: make -j64 from ToT.

Change-Id: Iadeac8d060cb693d4310afb841dc48d91f38597d