feat: setModelMenuBar accepts instance of MenusRegistry

[tlambert03]

This makes it possible to run setModelMenuBar(app.menus) to quick generate a menu bar with all menus in an application

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (0140de7) 100.00% compared to head (0488804) 99.55%.

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #139      +/-   ##
===========================================
- Coverage   100.00%   99.55%   -0.45%     
===========================================
  Files           31       31              
  Lines         1783     1796      +13     
===========================================
+ Hits          1783     1788       +5     
- Misses           0        8       +8     

Files	Coverage Δ
src/app_model/backends/qt/_qmainwindow.py	100.00% <100.00%> (ø)
src/app_model/backends/qt/_qmenu.py	93.49% <42.85%> (-6.51%)	⬇️

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[tlambert03]

need to consider this:
if you run this on the test app, you get menus: ['File', 'Edit', 'File/Open_From', 'Help']
the File/Open_From is a submenu... so it reveals that we can't just make the menu bar from all menus... we need a way for the user to be involved. And with that being the case, this becomes a bit less useful, and perhaps should stay as a draft until that issue is considered