rts/RtsSymbols: Add AArch64 outline atomic operations

Fixes #22012 (closed) by adding the symbols described in https://github.com/llvm/llvm-project/blob/main/llvm/docs/Atomics.rst#libcalls-atomic.

Ultimately this would be better addressed by #22011, but this is a first step in the right direction and fixes the immediate symptom.

Note that we dropped the __arch64_cas16 operations as these are not provided by all platforms' compilers.

Generated via $5733.

To do

• test to verify correctness of wrappers
• write Note