[WIP] Update APICompat baselines

[wtgodbe]

I got this by building once per-framework, and modifying shims.proj so that it writes to the baseline files rather than comparing against them. I remember there being some weirdness with that process, so I'm putting this up to see if CI complains before I look further.

[ericstj]

@wtgodbe why wouldn't these diffs have been causing APICompat failures before?

[wtgodbe]

@ericstj it looks like this just added a bunch of duplicates for some reason. I reduced ApiCompatBaseline.netcoreapp.netstandard.txt to just unique lines in Sublime, and it winds up being 2 lines shorter than the same in master. Not sure why that's happening yet.

[wtgodbe]

https://github.com/dotnet/corefx/pull/39033/files#diff-3093ac31dad3463a99acc3f2de5a439aL67 (and the next 2) appear to be the only real removals to ApiCompatBaseline.netcoreapp.netstandard.txt, while all the additions are duplicates. Presumably this is due to dotnet/standard#1181

[wtgodbe]

Removals from ApiCompatBaseline.netcoreapp.netstandardOnly.txt are legit, and are due to dotnet/standard#1222

[ericstj]

Yeah, I'm not worried about removals, that's cleanup. Additions indicate new problems that I would have expected to fail the build.

[wtgodbe]

Closing in favor of #39346