FileTreeView Status Bar

[Al12rs]

• Adds the total file count and file sizes in a Status bar at the bottom.
• Rewritten the code that creates the tree to remove some superfluous code
• Cleaned up code
• Added a File Count column (I can comment it out, mostly needed to test if the file counts were accurate)

Part of #1113

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 19.17808% with 236 lines in your changes are missing coverage. Please review.

Project coverage is 53.31%. Comparing base (38bb865) to head (8ac2201).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1124      +/-   ##
==========================================
- Coverage   53.52%   53.31%   -0.22%     
==========================================
  Files         676      677       +1     
  Lines       22525    22626     +101     
  Branches     1726     1725       -1     
==========================================
+ Hits        12057    12062       +5     
- Misses      10073    10172      +99     
+ Partials      395      392       -3     

Flag	Coverage Δ
Linux	52.64% <19.17%> (-0.21%)	⬇️
Windows	52.58% <19.17%> (-0.21%)	⬇️
clean_environment_tests	53.29% <19.17%> (-0.23%)	⬇️
macOS	52.08% <19.17%> (-0.24%)	⬇️
network_tests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ontrols/Trees/Files/FileTreeNodeDesignViewModel.cs	0.00% <0.00%> (ø)
...usMods.App.UI/Controls/Trees/IFileTreeViewModel.cs	0.00% <0.00%> (ø)
...pp.UI/Controls/Trees/ModFileTreeDesignViewModel.cs	0.00% <0.00%> (ø)
...p.UI/Controls/Trees/Files/FileTreeNodeViewModel.cs	0.00% <0.00%> (ø)
...rc/NexusMods.App.UI/Resources/Language.Designer.cs	47.74% <47.45%> (-0.83%)	⬇️
...Mods.App.UI/Controls/Trees/ModFileTreeViewModel.cs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

[Sewer56]

I've read through the code, but I'll make the remaining comments tomorrow, as I'm sleepy.

Good job with adjusting ModFileTreeViewModel constructor, you've managed to simplify it down a tiny bit more.