[memprof] Add a raw binary format to serialize memprof profiles.

This change implements the raw binary format discussed in
https://lists.llvm.org/pipermail/llvm-dev/2021-September/153007.html

Summary of changes
* Add a new memprof option to choose binary or text (default) format.
* Add a rawprofile library which serializes the MIB map to profile.
* Add a unit test for rawprofile.
* Mark sanitizer procmaps methods as virtual to be able to mock them.
* Extend memprof_profile_dump regression test.

Differential Revision: https://reviews.llvm.org/D113317