[clang] [AST][NFC] Rename checkFloatingPointResult to PointResultForOpportunisticFolding. (PR #213750)

[Timm Baeder via cfe-commits]

tbaederr wrote:

"opportunistic constant folding" is not a term we ever use. I don't even know what that's supposed to be.

https://github.com/llvm/llvm-project/pull/213750