dialects: (hw) Add hw.module.extern

[Moxinilian]

I factored a lot of logic out of hw.module in order to reuse it for this.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.64%. Comparing base (07266fc) to head (5054165).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2597      +/-   ##
==========================================
- Coverage   89.64%   89.64%   -0.01%     
==========================================
  Files         358      358              
  Lines       45359    45400      +41     
  Branches     6827     6835       +8     
==========================================
+ Hits        40663    40698      +35     
- Misses       3665     3669       +4     
- Partials     1031     1033       +2     

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