Add Intel APX support
Filing to track future work for supporting APX:

https://www.intel.com/content/www/us/en/developer/articles/technical/advanced-performance-extensions-apx.html

- 16 new GPR registers (so 32 total)
- REX2 prefix byte
- PUSH2/POP2: 2 at once
- Conditional load, store, cmp, test
- Option to suppress status flags of common instrs via EVEX prefix extensions of existing instrs

> Copied from https://github.com/DynamoRIO/dynamorio/issues/6226