Rename wasmi_ir::Instruction -> Op

[Robbepop]

This will likely simplify integration of #1650.

[codecov]

Codecov Report

❌ Patch coverage is 58.68393% with 383 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.77%. Comparing base (f7c77a7) to head (0e7d442).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/wasmi/src/engine/translator/func/visit.rs	43.12%	182 Missing ⚠️
crates/wasmi/src/engine/translator/comparator.rs	37.72%	170 Missing ⚠️
crates/wasmi/src/engine/translator/func/mod.rs	84.00%	12 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/simd.rs	14.28%	6 Missing ⚠️
crates/wasmi/src/engine/translator/func/simd/op.rs	0.00%	6 Missing ⚠️
...rates/wasmi/src/engine/translator/func/simd/mod.rs	70.00%	3 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/copy.rs	75.00%	1 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/return_.rs	75.00%	1 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/store.rs	0.00%	1 Missing ⚠️
crates/wasmi/src/engine/translator/utils.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1652      +/-   ##
==========================================
+ Coverage   70.65%   70.77%   +0.11%     
==========================================
  Files         179      179              
  Lines       15243    15199      -44     
==========================================
- Hits        10770    10757      -13     
+ Misses       4473     4442      -31     

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