Switch over the runtime outerloop pipeline to use Crossgen2

[trylek]

With this change, the only remaining pipelines using Crossgen1 are
"r2r.yml", "r2r-extra.yml" and "release-tests.yml". I haven't yet
identified the pipeline running the "release-tests.yml" script;
for the "r2r*.yml", these now remain the only pipelines exercising
Crossgen1. I don't think it makes sense to switch them over to
CG2 as we already have their CG2 counterparts; my expectation is
that, once CG1 is finally decommissioned, they will be just deleted.

Thanks

Tomas

/cc @dotnet/crossgen-contrib @dotnet/runtime-infrastructure

[mangod9]

Thanks for moving this over

[trylek]

Thanks Manish for the review. One more hurdle here is that this change is actually blocked on

#51416

as otherwise several outerloop tests fail on x86 and arm - we have always run the Crossgen2 outerloop tests on x64 / arm64 only, for 32-bit platforms we have just the "comparison runs" which apparently don't cover all the corner cases. I don't think it's super important to beef up the existing Crossgen2 testing as this PR is going to fill that coverage gap, it's just that we need to maintain the proper sequencing to keep CI healthy.

[trylek]

I have combined the change with the PR #51416 fixing the regression test 46239 and a few other issues as otherwise merging this in would break the outerloop runs with these errors.