[SanitizerBinaryMetadata] Introduce SanitizerBinaryMetadata instrumentation pass

Introduces the SanitizerBinaryMetadata instrumentation pass which uses
the new MD_pcsections metadata kinds to instrument certain types of
instructions and functions required for breakpoint-based sanitizers.

The first intended user of the binary metadata emitted will be a variant
of GWP-TSan [1]. GWP-TSan will require information about atomic
accesses; to unambiguously determine if an access is atomic or not, we
also require "covered" information which code has been compiled with
SanitizerBinaryMetadata instrumentation enabled.

[1] https://llvm.org/devmtg/2020-09/slides/Morehouse-GWP-Tsan.pdf

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D130887