[libc++] Consistently replace `::new(__p) T` with `::new ((void*)__p) T`. NFCI.

Everywhere, normalize the whitespace to `::new (EXPR) T`.
Everywhere, normalize the spelling of the cast to `(void*)EXPR`.

Without the cast to `(void*)`, the expression triggers ADL on GCC.
(I think this is a GCC bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98249)
Even if it doesn't trigger ADL, it still seems incorrect to use any argument
that's not exactly `(void*)` because that opens the possibility of overload
resolution picking a user-defined overload of `operator new`, which would be
wrong.

Differential Revision: https://reviews.llvm.org/D93153