[BOLT] Refactor relocation analysis code.

Summary:
Refactor the relocation anaylsis code.  It should be a little better at validating
that the relocation value matches up with the symbol address + addend stored in the
relocation (except on aarch64).  It is also a little better at finding the symbol
address used to do the lookup in BinaryContext, rather than just using symbol
address + addend.

(cherry picked from FBD6814702)