[BOLT] Sort BranchData in DataAggregator

Align perf reader to fdata behavior by sorting BranchData after reading samples,
in the same way as DataReader:
https://github.com/llvm/llvm-project/blob/20c66a0c66340f44f04b6526e45bcc5d872d480a/bolt/lib/Profile/DataReader.cpp#L1239

Namely, that order affects CallSiteInfo annotations which determine the
construction order of CallGraph, which in turn affects function reordering.

Reviewed By: #bolt, rafauler

Differential Revision: https://reviews.llvm.org/D152731