Re-factor linker code to use IR and be text format agnostic.

For header-abi-linker, convert text format specific code into IR code.
this gives us the benefit of being able to support multiple text formats

Bug: 63865902

Test: compared the linked abi dump for libbcinfo without this change and
with this change using header-abi-diff, found no differences.

Test: tests/test.py; all tests pass.

Change-Id: Iec05e85c1d6089c089e15acd7a05110d566fade5