Rename message args 💅 (backport #2207)

[mergify]

1. Rename args to msg consistently in WasmEngine interface
2. Rename file to wasm_engine.go to avoid the term "wasmer" in the wasmd codebase

   ---

   This is an automatic backport of pull request Rename message args 💅 #2207 done by Mergify.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.96%. Comparing base (6655b4a) to head (03f4952).
Report is 14 commits behind head on releases/v0.6x.

Additional details and impacted files

@@                Coverage Diff                 @@
##           releases/v0.6x    #2247      +/-   ##
==================================================
- Coverage           45.98%   45.96%   -0.02%     
==================================================
  Files                  78       78              
  Lines               10684    10684              
==================================================
- Hits                 4913     4911       -2     
- Misses               5334     5335       +1     
- Partials              437      438       +1     

Files with missing lines	Coverage Δ
x/wasm/types/wasm_engine.go	0.00% <ø> (ø)

... and 1 file with indirect coverage changes

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