Add ASAN coverage for all STL tests

[CaseyCarter]

... which isn't enabled in our typical CI, but will be part of a separate CI pipeline run on a different schedule. Probably daily or weekly - it's not terribly expensive - but not on every push into every PR.

The changes are broken down into focused commits:

1. Teach the test-case-gatherer to parse and filter by RunPL tags. Also change our single existing ctest test stl to only run configurations that do not have the ASAN tag. Add an additonal ctest test stlasan to run only configurations that do have the ASAN tag.
2. Calling this commit "focused" is a stretch: it adds ASan configurations to every test matrix we use, which is a fairly big lift. Runall is weird: when combining two configs via RUNALL_CROSSLIST, the result has the union of all variables present in either input configuration, with the value of each variable being the concatenation of the values from the inputs, and the intersection of the tags on the inputs. The special tag * is the identity element for tag intersection. So in every sequence of crosslists:

   meow
   woof
   RUNALL_CROSSLIST
   cat
   dog
   RUNALL_CROSSLIST
           seven    # No tag - not an ASAN test
   ASAN    eleven # ASAN tag - is an ASAN test
   

   Every configuration line before the final "leaf" RUNALL_CROSSLIST needs to be tagged with * or there will be no ASAN configurations in the resulting cross-product.
3. Update the libc++ expected_results.txt file. The :0 config is the same as before, but :1 is now the MSVC-ASAN configuration and :2 is clang-cl. (I think it's less confusing in the long term to change the clang-cl assignment than to have the two MSVC tags be non-consecutive.) This generally looks like "change :1 to :2, and then duplicate the :0 entries with :1", but there are some :0s with no corresponding :1 for failures due to /analyze bugs - we don't run /analyze together with /fsanitize=address.
4. A specific change to the P0881R7_stacktrace test. The source_location values that this test observes are affected by the presence of /Zi on the command line; since /fsanitize=address is always paired with /Zi, the ASAN configuration(s) HAS_DEBUG_INFO even when it's not specified on the command line.
5. Add a no-ASAN version of fast_matrix for three <regex> tests that leak memory when compiled with ASAN.
6. Changes to the Azure Pipelines infrastructure. This adds a new azure-devops/asan-pipeline.yml for the new pipeline which has been running against my fork (https://dev.azure.com/vclibs/STL/_build?definitionId=5&_a=summary) during development, but will be retargeted after this PR merges. The new pipeline looks a lot like the old one, but with a different default value for the testSelection variable which is plumbed through into the run-tests.yml template to select which tests to run.

This is a dual of internal MSVC-PR-500092.

[StephanTLavavej]

There are a couple of places where you fused env.lst lines that had been written somewhat verbosely in an attempt to keep different files looking similar (the header units, modules, and floating-point matrices), but it's not worth resetting testing either, and arguably attempting to keep files looking similar without explicit comments was a lost cause anyways.