Normalize path (slashes to be precise) when opening a database or saving the last used database paths (Fixes #7821)

[HusseinKabbout]

This PR fixes the funny behavior described in issue #7821.

To summarize, depending on how you load a database in Windows, you will find the path (to the database) twice in the Recent Databases menu entry. The only difference between the two entries would be the slashes.

Testing strategy

As I don't have a windows environment to test this small change, I don't really know how to test it for windows (because it is a windows only bug). So my question here is, how do you test your code for linux and windows?

Type of change

• ✅ Bug fix (non-breaking change that fixes an issue)

[phoerious]

Thanks!
I think you need to add the explicit include to the other file as well, though. There are also some code formatting issues, but other than that, lgtm.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 64.31%. Comparing base (5916a8f) to head (0e00699).
Report is 444 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/gui/MainWindow.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7864      +/-   ##
===========================================
+ Coverage    64.31%   64.31%   +0.01%     
===========================================
  Files          339      339              
  Lines        43404    43430      +26     
===========================================
+ Hits         27911    27930      +19     
- Misses       15493    15500       +7     

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