Investigate global font scale in MonoGame

[vchelaru]

Is it functional? If so, we need to update the documentation to show how it works.

[vchelaru]

Done, but now it needs documentation.

[vchelaru]

Guide font should not be affected by global font scale - set a font scale inverse to that value.

[vchelaru]

Documented: https://docs.flatredball.com/gum/gum-tool/editor-tab#font-scale