Migrate Window menu to app-model

[lucyleeow]

References and relevant issues

Follow on from #4977, new PR to avoid bad merging due to conflicts.

Changed file test_viewer_toggler.py filename to test_togglers.py and added a test for the new DockWidgetToggleAction

Description

Migrate window menu to app-model

[lucyleeow]

cc @DragaDoncila

[codecov]

Codecov Report

Attention: Patch coverage is 98.07692% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 92.44%. Comparing base (a9c25e6) to head (844bcfc).
Report is 1 commits behind head on main.

Files	Patch %	Lines
napari/_qt/qt_main_window.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6905      +/-   ##
==========================================
- Coverage   92.45%   92.44%   -0.02%     
==========================================
  Files         614      614              
  Lines       55166    55192      +26     
==========================================
+ Hits        51002    51020      +18     
- Misses       4164     4172       +8     

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