any support on MinGW and UTF-8 character display

[DickyQi]

Nice work!!!🤭
I have two requirement.

1. build for Linux/MacOS is working fine now, still need Windows support base on MinGW env, is it possible？
2. need display UTF-8 character on terminal such like Chinese/emj character.

Thanks for your working again!!!

[nealmick]

Okay i have merged in MSVC and MinGW support in pr #3. UTF-8 Characters on windows are rendering so long as they are in the font atlas. You can change what font is loaded in config-imgui.h.

There are still a few bugs on windows with emoji and other wide characters causing issues.
As far as I can tell Mintty(MinGW's emulator) and the windows terminal both have similar issues with emojis taking up multiple char cells, and sometimes leaking utf8. The issues stem from ConPty and affect many terminal emulators. On the surface it would seem possible to solve some of the issues however any TUI app such as vim or neovim would also need to be patched. Concretely apps like neovim derive the cursors position internally and the emulator has no control over whether vim treats an emoji character as a single cell, multiple, or a wide cell (wcwidth). For now I am going to leave windows support for CJK and Emoji where it is as I do not see a clear solution for windows. With this PR the emulator will render any UTF8 character in the font atlas, however behavior around those characters such as how many cells they take up is undefined on windows and depends on the environment your running in.