Foldable panel sections

[MinusGix]

• Added an entry to CHANGELOG.md if this change could be valuable to users

This PR allows you to fold panel sections. It also introduces a PanelBuilder structure to share the logic between different panels, which can hopefully be extended in the future to allow resizing panel sections.

This does have an issue when folding the panel when it is on the bottom that I'm not 100% on how to fix. It makes so the one that is folded takes more space...

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 210 lines in your changes are missing coverage. Please review.

Project coverage is 5.92%. Comparing base (43b54d0) to head (c29e5e5).
Report is 41 commits behind head on master.

Files	Patch %	Lines
lapce-app/src/panel/view.rs	0.00%	112 Missing ⚠️
lapce-app/src/app.rs	0.00%	49 Missing ⚠️
lapce-app/src/panel/debug_view.rs	0.00%	16 Missing ⚠️
lapce-app/src/panel/problem_view.rs	0.00%	14 Missing ⚠️
lapce-app/src/file_explorer/view.rs	0.00%	11 Missing ⚠️
lapce-app/src/panel/plugin_view.rs	0.00%	4 Missing ⚠️
lapce-app/src/panel/source_control_view.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #3086      +/-   ##
=========================================
- Coverage    6.01%   5.92%   -0.10%     
=========================================
  Files         122     122              
  Lines       42703   43413     +710     
=========================================
+ Hits         2569    2572       +3     
- Misses      40134   40841     +707     

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