Move FuncTranslator internals into func submodule of translator module

[Robbepop]

These changes make it simpler for #1512 to build an alternative FuncTranslator.

No logic is modified in this PR, only code is moved around. That's why the diff is so big.

[codecov]

Codecov Report

Attention: Patch coverage is 90.19608% with 5 lines in your changes missing coverage. Please review.

Project coverage is 71.76%. Comparing base (2254f91) to head (b6e14c5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/wasmi/src/engine/translator/utils.rs	0.00%	3 Missing ⚠️
crates/wasmi/src/engine/translator/func/utils.rs	95.83%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1532      +/-   ##
==========================================
+ Coverage   71.75%   71.76%   +0.01%     
==========================================
  Files         177      179       +2     
  Lines       16524    16524              
==========================================
+ Hits        11857    11859       +2     
+ Misses       4667     4665       -2     

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