transformations: add convert-arith-to-riscv-snitch pass

[superlopuh]

Lets us handle the packed SIMD operations.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.90%. Comparing base (e863366) to head (d48500f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2914      +/-   ##
==========================================
- Coverage   89.90%   89.90%   -0.01%     
==========================================
  Files         403      404       +1     
  Lines       50424    50478      +54     
  Branches     7788     7797       +9     
==========================================
+ Hits        45334    45380      +46     
- Misses       3862     3866       +4     
- Partials     1228     1232       +4     

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[zero9178]

Suggested change

	// CHECK: builtin.module
	// CHECK-NEXT: %l, %r = "test.op"() : () -> (!riscv.freg, !riscv.freg)
	// CHECK: builtin.module
	// CHECK-NEXT: %[[L.*]], %[[R:.*]] = "test.op"() : () -> (!riscv.freg, !riscv.freg)

Since 9b43500 landed, does this mean we can use named SSA variables now?

[superlopuh]

Why do it in this case if the variable names are stable and more readable?

[superlopuh]

I'll merge for now since you've approved but happy to refactor tests together tomorrow, there's more to come