[libcxx] [llvm] [libc++] Remove `get_temporary_buffer`/`return_temporary_buffer` (PR #100914)

[Nikolas Klauser via llvm-commits]

https://github.com/philnik777 commented:

I like this a lot more than the previous version. Let's see what Louis thinks.

https://github.com/llvm/llvm-project/pull/100914