Font scaling (mostly for Linux)

[Necoro]

DO NOT MERGE BLINDLY

As stated in #437, currently no font scaling happens on Linux, but it seems to be needed. This PR wants to look into this issue a lil' bit...

Changes in this PR:

• enable font scaling on Linux (and technically also Mac, but GetContentScale always returns 1 there)
• Fixed: when scaling was used, extraFonts would not load, because the scaled size was written as a key.

Open points so far:

• if I see this correctly, DPI settings are not updated. I.e. when moving the window to another monitor with other DPI settings, those do not apply. Shall this be fixed, or is this intended?
• there is also a call to style.ScaleAllSizes in MasterWindow.go#setTheme, that is only executed on Windows. Enabling this also in Linux -- shows no difference. What should I expect here?

@macbutch, @HACKERALERT: As you were also dealing with DPI scaling issues (#350), do you have any input here? What platforms were you on?

[codecov-commenter]

Codecov Report

Merging #441 (af164d2) into master (eb9f90e) will increase coverage by 0.00%. The diff coverage is 0.00%.

@@          Coverage Diff           @@
##           master    #441   +/-   ##
======================================
  Coverage    2.91%   2.91%           
======================================
  Files          30      30           
  Lines        3122    3121    -1     
======================================
  Hits           91      91           
+ Misses       3031    3030    -1     

Impacted Files	Coverage Δ
FontAtlasProsessor.go	0.00% <0.00%> (ø)
canvas.go	0.00% <0.00%> (ø)
msgbox.go	0.00% <0.00%> (ø)
markdown.go	0.00% <0.00%> (ø)
ExtraWidgets.go	0.00% <0.00%> (ø)
ImageWidgets.go	0.00% <0.00%> (ø)
utils.go	29.80% <0.00%> (+0.28%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update eb9f90e...af164d2. Read the comment docs.

[HACKERALERT]

I've really only tested on Windows. I compile giu programs on macOS and Linux, but since I do it via VirtualBox which doesn't support OpenGL, I can't see what the compiled program looks like. So I probably can't lend much wisdom here.

[gucio321]

@Necoro may I ask what is stat of this PR right now? It looks like it is draft since over a year...

[Necoro]

@gucio321 I used the my changes in my private build on Linux and Windows and it worked. But it was along the lines of "I dont really know what I'm doing".

The projects I used it in where one-shot uses (more or less) and I do not use giu anymore. Therefore I've not that much motivation on porting the patch to the current HEAD.

If in doubt, close this PR. The changes are rather minor and can easily be re-done by any interested party.

[gucio321]

I see. So I think it should be marked as ready-for-review. But @AllenDang could you take a look? I don't know what it does too :smile:

[gucio321]

closing due to age and #628