Support bit offsets in struct members (IDA)

[mahaloz]

Since #118, it's become clear we do not support structs that have members at bit offsets:

libbs/libbs/decompilers/ida/compat.py

Line 1013 in ce14917

# TODO: warning if offset is not a multiple of 8 (a bit offset), we are in trouble

Tasks

To close this issue, these things need to happen

• Change the definition of Struct and StructMember Artifacts to be bit offsets for members
• Update IDA Pro backend to support bits
• Make new issues for each decompiler that does not have easy support for bit offsets in structs