Add test and benchmark.
Also switch libbacktrace, libunwindstack, libmemunreachable
to use libprocinfo for map file reading.
The benchmark shows using libprocinfo speeds up map file reading
in libbacktrace and libunwindstack 18% - 36% on walleye.
Bug: http://b/79118393
Test: run procinfo_test.
Test: run libunwindstack_test.
Test: run libbacktrace_test.
Test: run memunreachable_test.
Change-Id: Icf281c352f4103fc8d4ba6732c5c07b943330ca1
Add a new library for parsing /proc files. Start with helpers for
parsing /proc/<pid>/status and /proc/<pid>/task.
Bug: http://b/30705528
Test: libprocinfo_test32/64 on host/bullhead
Change-Id: I5757514c0aede8a9d75834b55aae42a5cf762b95
