[memprof] Accept a function name in YAML (#119453)
This patch does two things:
- During deserialization, we accept a function name as an alternative
to the usual GUID represented as a hexadecimal number.
- During serialization, we print a GUID as a 16-digit hexadecimal
number prefixed with 0x in the usual way. (Without this patch, we
print a decimal number, which is not customary.)
In YAML, the MemProf profile is a vector of pairs of GUID and
MemProfRecord. This patch accepts a function name for the GUID, but
it does not accept a function name for the GUID used in Frames yet.
That will be addressed in a subsequent patch.
