Allow adding class/struct members to padding space

This commit removes the comparison between class size and member offsets
from RecordTypeDiffIR::IsExtended. New members can be added to padding
space in a class without changing the existing members.

Test: ./test.py
Bug: 248418092
Change-Id: I34d002478f1dcfd3c183e76899917e602de2b4c1
5 files changed