Fix terminal/screenshot related bugs

[vintagepc]

Description

Fixes some GL related bugs with the terminal and screenshot scaling.

Behaviour/ Breaking changes

Terminal no longer vanishes when scaling
Screenshots created using the hotkey now respect the actual scaled window size.

Linked issues:

• Closes [FEATURE] Screenshot should scale.  #335
• Closes [BUG] Terminal is glitched on standalone MMU2 and when resizing.  #333

[codecov]

Codecov Report

Merging #336 (016769d) into master (029cc59) will decrease coverage by 0.02%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##           master     #336      +/-   ##
==========================================
- Coverage   90.95%   90.92%   -0.03%     
==========================================
  Files         162      162              
  Lines        7515     7517       +2     
==========================================
  Hits         6835     6835              
- Misses        680      682       +2     

Impacted Files	Coverage Δ
MK404.cpp	86.32% <0.00%> (ø)
parts/components/GLHelper.cpp	83.49% <33.33%> (-1.51%)	⬇️
parts/printers/Prusa_MMU2.cpp	88.88% <100.00%> (-1.12%)	⬇️

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