gui: Improve font atlas

[Macdu]

• Make the font 4 times more detailed on default settings. They should look a lot less blurry on a high-definition display and the atlas still fits in a 4096x4096 texture.
• Remove the whole Unified ideograms CJC characters from the default configuration. They take more space than everything else combined and should not be here to begin with
• Use ImGui fonctions for korean, simplified and full chinese ranges