Add Thai language support

[nProtect]

Add Thai language support via GetGlyphRangesThai()

[ocornut]

Thanks! To apply the PR as-is with your login/commit name please try to follow the coding convention of ImGui (spaces after //, 4-spaces instead of tabs).

[nProtect]

OK I have changed tab to spaces. Thanks for recommend me.

[ocornut]

I have merged it now and applied fixes. Please pay more attentions when submitting PR in order to make it easier for the project manager to merge changes.

• rebase-squashed your 4 commits into ones
• it was missing spaces after //
• it was still using lots of tabs in imgui_draw.cpp
• there was a typo

4141144
8efd05a

Thanks!

[ocornut]

#8465 is making the use of glyph range functions unnecessary, so GetGlyphRangesThai() will eventually be removed once the work on dynamic_fonts is over.