Move PC-only unwind frame generation to libunwindstack.

GWP-ASan uses frame-pointer based unwinding internally on
allocation/deallocation to collect stack traces that are used when
crashes are reported.

This should be generic, so pull it out into libunwindstack so it can be
used by MTE as well.

Bug: 152412331
Test: atest debuggerd_test
Change-Id: I27b32263aac63446f5fe398af108676b70cd3971