[NFC][compiler-rt][hwasan] Move allocation functions into their own file

This removes the `__sanitizer_*` allocation function definitions from
`hwasan_interceptors.cpp` and moves them into their own file. This way
implementations that do not use interceptors at all can just ignore
(almost) everything in `hwasan_interceptors.cpp`.

Also remove some unused headers in `hwasan_interceptors.cpp` after the move.

Differential Revision: https://reviews.llvm.org/D103564