Enable SDL_HINT_IME_SHOW_UI to make typing CJK not guesswork

For some reason, the default behavior of SDL and/or Windows(?) (I only
tested this on Windows) seems to result in the fact that if any SDL app
doesn't account for it, there is no way for Japanese and Chinese
speakers to know what they're typing in.

How IMEs are supposed to work is that you can type words as sort of
WIP versions, and then select out of a list of candidates what the
final result should be. The app may display the WIP text and tell the
IME where the text field is so that the IME's menu can be displayed
around it. But if the app doesn't say where the text field is, then the
candidate list can also be displayed at the corner of the screen, which
is done in Minecraft.

By default, however, SDL apps don't get a candidate list at all, which
means you're basically flying blind as to what you're typing in, and
you would have to basically open notepad and copy-paste everything from
there - unless I'm missing something.

This commit sets the SDL_HINT_IME_SHOW_UI hint (added in SDL 2.0.18
apparently), so that the candidate list is at least shown in the corner.
We can probably deal with positioning and uncommitted text later.

desktop_version/src/main.cpp

@@ -556,6 +556,8 @@ int main(int argc, char *argv[])
     }
 #endif
 
+    SDL_SetHintWithPriority(SDL_HINT_IME_SHOW_UI, "1", SDL_HINT_OVERRIDE);
+
     if(!FILESYSTEM_init(argv[0], baseDir, assetsPath, langDir, fontsDir))
     {
         vlog_error("Unable to initialize filesystem!");