[clang] [clang] Implement CWG2851: floating-point conversions in converted constant expressions (PR #90387)

[Mital Ashok via cfe-commits]

MitalAshok wrote:

Waiting on #90352 because it's not on the cxx_dr_status page yet (`make_dr_status` doesn't do anything)

https://github.com/llvm/llvm-project/pull/90387