[BOLT] Sort CallSiteInfo targets by symbol name in YAMLWriter

Align YAML and fdata profiles by sorting CallSiteInfo targets by symbol name,
aligning it to fdata. By default, YAML CallSiteInfo is sorted by function id,
which is the order of function in the binary.

Follow-up to D152731, aligning yaml vs fdata, and in turn all three between to
each other.

Reviewed By: #bolt, rafauler

Differential Revision: https://reviews.llvm.org/D152733