[TableGen] Reduce size of MatchTableRecord (NFC) (#125221)
MatchTableRecord stores a 64-bit RawValue. However, this field is only
needed by a small part of the code (jump table generation).
Create a separate RecordAndValue structure that is used in just the
necessary places.
Based on massif, this reduces memory usage on RISCVGenGlobalISel.inc by
about 100MB (to 2.15GB).
