Implemented drawing of CJK characters with ImGui screens

[katemonster33]

Summary

Bugfixes "Implemented drawing of non-English characters in ImGui screens"

Purpose of change

Fixes: #72162

Describe the solution

Implemented a font "fallback" system in ImGui to allow CDDA to interrupt ImGui's drawing flow to draw glyphs using CDDA's Font::OutputChar method.

Describe alternatives you've considered

There are open PRs in the ImGui repo that implement dynamic font atlases which could potentially solve this problem, but they seem far from being viable enough to be a better solution than this.

Testing

Changed the language to Chinese, opened up the keybindings screen, and verified that the screen displays properly

Additional context

The 'x' and 'y' position that ImGui tries to draw at doesn't quite work for Cataclysm. I needed to modify those by magic numbers to make the font align properly. I'm still not sure why it's needed.

[katemonster33]

Just noticed something... On text entered into an input field, the cursor position doesn't match the space between glyphs

Edit: with CJK characters I mean

[katemonster33]

Just noticed something... On text entered into an input field, the cursor position doesn't match the space between glyphs

Edit: with CJK characters I mean

this should be good now

[ZeroInternalReflection]

I distinctly recall this PR having a note requesting Curses testing, but I'm apparently confusing that with a different PR. Regardless, I'd call the impact on the Curses build "unfixed, but a step in the right direction".
In the current state of things, ImGui windows will print out a bunch of garbage instead of the appropriate characters (Simplified Chinese pictured):

After this PR, any unhandled glyphs instead print out as blank space:

Notably, the blank space appears to be the appropriate size for the unprinted text, so it looks like the character width calculations are working. Contrast the Chinese above with Russian below:

[katemonster33]

I distinctly recall this PR having a note requesting Curses testing, but I'm apparently confusing that with a different PR. Regardless, I'd call the impact on the Curses build "unfixed, but a step in the right direction". In the current state of things, ImGui windows will print out a bunch of garbage instead of the appropriate characters [...]

This is a good catch. The fault for the original issue likely lies in the ImTui backend. I definitely wouldn't expect this PR to fix it unfortunately, since this has everything to do with graphical textures that curses builds know nothing about.

I would go ahead and make a separate issue for that, we will need to track that as a blocker for moving the UI completely to ImGui.