yksmp could use abstraction

[vext01]

There are lots of places in our codebase where raw DWARF register numbers are used. That might have been OK if we had only one numbering scheme, but since we use dynasm and that has a different numbering scheme, it might be worth doing some abstraction to give the numbers symbolic names.

Examples of places that would need attention:

• 40fc3dd

• yk/ykrt/src/compile/jitc_yk/codegen/x64/mod.rs

  Line 839 in 6acca9f

  fn cg_loadtraceinput(&mut self, iidx: jit_ir::InstIdx, inst: &jit_ir::LoadTraceInputInst) {

• ...

(please add more as you encounter them)

[ltratt]

s/might be worth doing/absolutely 100% definitely unconditionally without-a-shadow-of-a-doubt must do/