[clang] [clang-cl] [Sema] Support MSVC non-const lvalue to user-defined temporary reference (PR #99833)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman requested changes to this pull request.

Thank you for this! I think there's some work left to be done though.

1) Please add an extension warning (and tests for it) so users know where the extension is being used even if they opt into it explicitly. This is important for `-pedantic` mode.
2) This should be controllable via `-fms-extensions`/`-fno-ms-extensions`; having its own dialect flag is a bit novel but I'm not strongly opposed. CC @MaskRay @jansvoboda11 for driver/options opinions
3) Please document the extension in `clang/docs/LanguageExtensions.rst`

https://github.com/llvm/llvm-project/pull/99833