Feature/set meson b_vscrt with clang-cl

[lukester1975]

Changelog: Feature: Ensure meson toolchain sets b_vscrt with clang-cl.
Docs: Omit

This is a follow up to ##13424 (comment), specifically item 3.

• The if compiler in ("msvc", "clang") is a bit ugly but as I mentioned in the issue, I couldn't see a way to see if the compiler is really clang-cl at that point. Safe enough given the msvc_runtime_flag implementation (note I changed it to return None for all non-compiler.runtime cases such that _b_vscrt is consistently None; all other usages seem OK with that).
• Given that, arguably the if compiler in ("msvc", "clang") test could be removed. Intel's cl-like frontend?
• In the tests I couldn't get the VS17/clang16 pytest.mark.tool working, so they are commented out. I'm sure I'm just missing some magic incantation somewhere despite VS2022 being enable in my env.
• VS 17.7 has bumped clang from 15 -> 16. So I guess if the test runners aren't updated, these tests may fail. I use a jinja profile for clang-cl with this hack: compiler.version={{ os.popen("clang-cl --version").read().removeprefix("clang version ").split(".")[0] }}. I guess this could do something similar if necessary?

• Refer to the issue that supports this Pull Request.
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

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