namespace sts::ams -> ams::exosphere, ams::.

This is to facilitate future use of ams:: namespace code in
mesosphere, as we'll want to include ams::util, ams::result, ams::svc...

Because I was working on multiple things at once, this commit also:
- Adds wrappers for/linker flags to wrap CXX exceptions to make them
  abort. This saves ~0x8000 of memory in every system module.
- Broadly replaces lines of the pattern if (cond) { return ResultX; }
  with R_UNLESS(!cond, ResultX());.
- Reworks the R_TRY_CATCH macros (and the result macros in general).

Quite a few headers are unused in this header, so we can remove them to
make compilation a tiny bit faster.

Prevents potential inclusion issues.