[memprof] Don't use Frame::hash() (NFC) (#119828)
In these tests, we just want to add one instance of
IndexedMemProfRecord to MemProfData.Records and retrieve it from
MemProfReader. There is no particular reason to associate F1.hash()
with the IndexedMemProfRecord instance. A fake value suffices.
While I am at it, I'm switching to try_emplace so that I can move
FakeRecord.
