Make CJK IMEs work better

[Soreepeong]

Japanese IME	Korean IME

Changes

• When using CJK IMEs, it will use SeIconFont to display the current input mode. Only applicable when current thread keyboard layout (=input method) is one of CJK, regardless of variants (trad/simplified/hk/etc.)
• When using Japanese IME, it will display correctly segmented candidate selector display.
• When using Korean IME, it will stop randomly dropping characters on all the random occasions you can imagine.
• IME windows will now show in other viewports too.
• IME will not stop working when changing across viewports.

Someone should test Chinese IMEs. This probably should work because Chromium had the least amount of special-casing for Chinese IME among CJK IME handling code, but better make sure.

[goaaats]

@Bluefissure would you mind testing this PR with a Chinese IME?

[Bluefissure]

@Bluefissure would you mind testing this PR with a Chinese IME?

Sure, I have a bunch of meetings this evening so probably I need to test after the meetings.

[nebel]

I tested these changes against the Japanese issues listed in #1498 and it seems to fix both of them (simultaneous input problem, and the "stuck in alphabetic mode" problem).

There is still a small issue where, if there is an active input (i.e. blinking cursor) in a native game input, and we switch to an imgui input, then both completion windows will appear as text is typed since both inputs are kind of simultaneously active (and if there is a completion active already when focus is changed, those completion options will also carry over to the imgui input completion). This only happens one-way as switching to a native game input will clear imgui focus, but not vice-versa. However, selecting a completion will only add it to the actually active input, so I think this is a very minor issue and not worth holding back these changes.

[Bluefissure]

It's working fine in Microsoft Pinyin (Chinese IME) as:

It also fixes ottercorp#39

[Soreepeong]

@Bluefissure Now that you're testing it, can you test if Latin character input mode displays its corresponding symbol "英"? Since Japanese IME had different condition for that compared to Korean, need to check if Chinese IME works like Korean IME or Japanese IME.

[Bluefissure]

@Bluefissure Now that you're testing it, can you test if Latin character input mode displays its corresponding symbol "英"? Since Japanese IME had different condition for that compared to Korean, need to check if Chinese IME works like Korean IME or Japanese IME.

Yes it shows "英" in Latin mode of Microsoft Pinyin

and "中" for Chinese mode

and shows nothing when I turn the IME off

[Soreepeong]

Sounds good enough then!