[HWASAN] Update dbg.assign intrinsics in HWAsan pass (#79864)

llvm.dbg.assign intrinsics have 2 {value, expression} pairs; fix hwasan to
update the second expression.

Fixes #76545. This is #78606 rebased and with the addition of DPValue handling.
Note the addition of --try-experimental-debuginfo-iterators in the tests and
some shuffling of code in MemoryTaggingSupport.cpp.