Avoid evil macros

[StephanTLavavej]

ICU previously macroized these reserved names. This was fixed by unicode-org/icu#1555 on 2021-02-01, but old versions of ICU are still being used by various projects. Let's avoid these names for now. I haven't added test coverage because the UCRT uses some of these reserved names (which it's getting away with, due to the specific order in which headers are being included).

Fixes VSO-1837381 "[RWC][prod/fe][Regression] PDFium failed with error C2209: 'std::_Aligned_storage_t<64,8>': aliases cannot be used in constructor declarations".

• _Cs => _Cs_storage
  • This introduces a slight but acceptable asymmetry with mutex.cpp.
  • This is the actual fix for the regression introduced by <mutex>: Make _Mtx_internal_imp_mirror more closely match _Mtx_internal_imp_t #3763. We were getting away with the others.
• _No => _Nope
  • This makes <deque> _Is_bidi consistent with <format> _Add_newline, <xlocale> _Case_sensitive, etc.
• _Mn => _Min_, also _Mx => _Max_ for consistency
  • This is our conventional pattern for avoiding parameters shadowing data members.
• _Cc => _Cx, also _Yy => _Yx and _Nn => _Nx for consistency
  • This is our common pattern for "single letter" variable names.
• _Pi => _Pi_val

[StephanTLavavej]

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