Various cleanups

[StephanTLavavej]

• Enable clang-format in many places with zero-to-minor changes.
  • It's getting better at handling concepts.
• Add newlines between non-chained if statements.
  • This convention makes it easier to see where new chains of tests begin.
• Change __analysis_assume to _Analysis_assume_.
  • This is for consistency - they're equivalent, but we should use the more "modern" form.
• <algorithm>: Fix an unpaired // clang-format off after _Generate_n_fn.
• <complex>: Centralize on using _STD instead of ::std::.
  • This is more searchable, and may matter in the distant future.
• <complex>: Remove unnecessary _STD qualification on an _Ugly function, _Log_abs().
• <limits>: Remove unnecessary qualification of std::numeric_limits.
• <locale>: Remove unnecessary defenses for macroized isalnum etc.
  • Followup to <cctype>: do not defend against isalnum/etc. macros #2147.
• <random>: Use range-for.
  • Use _Val, as _Elem is almost always a template parameter here.
• <random>: Improve formatting of _Refill_lower().
• <random>: Slightly simplify loop in _Small_poisson_distribution::operator().
  • This slightly changes control flow, but with identical behavior.
  • Use initializers instead of assignments with a comma operator.
  • Directly return instead of break followed by return. (There's no other way to exit this loop.)
  • Scope _Res to the loop, making its counting behavior even clearer.
• <ranges>: Use extended friend syntax.
  • We prefer this because it's shorter and avoids any possibility of declaring stuff.
• <yvals_core.h>: Cite <cuchar>: mbrtoc8() and c8rtomb() are not yet implemented #2207 for mbrtoc8() and c8rtomb().
• <yvals_core.h>: Remove dead macro _STL_WIN32_WINNT_WINXP.
• Rename 💥 to 🐶 etc., following our current policies.
• Rename to GH_001411_core_headers/test.compile.pass.cpp.
  • This tells the Python-powered test harness to not bother executing this // COMPILE-ONLY test.
• P0912R5_coroutine/test.cpp: Simplify __cpp_lib_coroutine test.
  • After VS 2019 16.9 Preview 1 toolset update #1451, it's either defined to its modern value or not at all:

    STL/stl/inc/yvals_core.h

    Lines 1257 to 1259 in ff54450

    	#ifdef __cpp_impl_coroutine
    	#define __cpp_lib_coroutine 201902L
    	#endif // __cpp_impl_coroutine

• P0980R1_constexpr_strings/test.cpp: Attach a brace to test_gh_2524().
• VSO_0102478_moving_allocators/test.cpp: Pass format strings directly to printf.
  • This allows the compiler to detect type mismatches.
• Delete flaky skipped tr1 tests.
  • Suggested by @AlexGuteniev - we have no intention of salvaging these tests. If we wanted better coverage in these areas, we'd write new tests from scratch.
• P0083R3_splicing_maps_and_sets/test.cpp: Drop special case for Clang.
  • Suggested by @fsb4000. This test is for C++17 and above. Clang 10 added support for C++20 constinit, so we can drop the special case here. (We don't need special coverage for C++17 specifically here.)
• Update comments to // TRANSITION, Clang 14 coroutine support.
• P0912R5_coroutine/env.lst: Add MSVC/EDG C++20 and Clang C++23 coverage.
• Update comments and test coverage for /await:strict.
  • Thanks to @cpplearner for noticing this. Coroutines are usually C++20 but are also activated by /await:strict, so we permanently need to check __cpp_impl_coroutine - this is not a temporary thing until Clang 14 is released. (Tests that are C++20-specific can be simplified after Clang 14, so they still have TRANSITION comments.) Finally, we should also add a new configuration to VSO_0157762_feature_test_macros.
• VSO_0157762_feature_test_macros/env.lst: Remove unused configurations.
  • These configurations were unused after Remove compiler specific feature test macro tests #752.

If desired, I can split this into smaller PRs, but I believe that the changes are simple enough to be reviewed in a single PR.

[StephanTLavavej]

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