/azp run STL-ASan-CI

How can you remove workarounds without updating internal build?

That's a good question! (And one that I didn't fully think through before submitting this PR 😹)

In this case I think I'll get away with all of these workaround removals. EDG is updated independently from the checked-in MSVC toolset, and is actually usually a newer version than what's shipping publicly, so the EDG workaround removals should be fine. The <limits.h> workaround removal depends on updated VCRuntime sources that I fixed, which are present in the internal repo (they aren't consumed from the checked-in toolset). So that leaves the ASAN issue, which I think will be okay - the checked-in toolset is used only for the initial build, whereas the tests run with the freshly built compiler. Even though we're building the compiler with ASAN these days (or will shortly, I forget), this bug was specific to the static debug STL, but the compiler doesn't consume the STL statically.

I'm speculatively mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.