[clang] Fix consteval initializers of temporaries

When a potential immediate invocation is met, it is immediately wrapped by a
`ConstantExpr`. There is also a TreeTransform that removes this `ConstantExpr`
wrapper when corresponding expression evaluation context is popped.
So, in case initializer was an immediate invocation, `CXXTemporaryObjectExpr`
was wrapped by a `ConstantExpr`, and that caused additional unnecessary
`CXXFunctionalCastExpr` to be added, which later confused the TreeTransform
that rebuilds immediate invocations, so it was adding unnecessary
constructor call.

Fixes https://github.com/llvm/llvm-project/issues/60286

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D146801