Support "memtag_heap" sanitizer.

Memtag_heap adds an ELF note that enables MTE heap tagging in
bionic/scudo. Ignored on non-executables. With diagnostic
(diag:{memtag_heap:true}) enables the SYNC mode, otherwise - ASYNC mode.

Memtag_heap defaults to set (with diag) on cc_test targets, unset
otherwise. Ignored on non MTE-compatible hardware.

Bug: b/135772972
Test: soong tests

Change-Id: I88fd0f159e609e17bd13487749980a1ba02cb91c