Flatlaf UI scaling

[SJuliez]

This PR

• adds GUI scaling to MML. It uses FlatLaf scaling rather than the manual scaling of MM, so the scaling itself is just a single System.setProperty call
• removes all hardcoded sizes of elements as those interfere with scaling; these are replaced with "prototype" values/components that fix the size in a scale-friendly way
• adds a setting to the options dialog. This works with MM's GUIPreferences gui scale setting rather than MML's own settings as I assume that separate gui scale values will not work for a combined install anyway so might a well use a single value
• fixes a minor thing or two, e.g. the selected theme was not correctly checked in the menu upon startup

MML at a rather silly scale relative to the taskbar:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.15%. Comparing base (04e239e) to head (5785bc8).
Report is 19 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##             master   #1610      +/-   ##
===========================================
+ Coverage      2.13%   2.15%   +0.01%     
- Complexity      204     205       +1     
===========================================
  Files           266     266              
  Lines         30697   30623      -74     
  Branches       5231    5234       +3     
===========================================
+ Hits            656     660       +4     
+ Misses        29888   29810      -78     
  Partials        153     153              

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[HammerGS]

I tested this pre-Mek merge and it was working great.