Add linker_set_key to RecordTypeDiff and EnumTypeDiff

RecordTypeDiff and EnumTypeDiff in abi_diff.proto contain linker set
keys. The developers can copy them to the ignore list. The other Diff
messages do not need the field because it's in the messages imported
from abi_dump.proto.

Test: Update prebuilts/clang-tools; make libz
Bug: 243903630
Change-Id: I1e90d3c6cbfd09d72b3fdb244a4079ae899630aa
4 files changed