Treat "/" as a key that should be evaluated by the Win IME system when
the input language is Chinese. This fixes a duplication of the input
character and results in the expected output of a Chinese wide comma.

When using Windows and entering Chinese characters using the Pinyin IME, pressing forward slash should result in a "、", Unicode character "Ideographic Comma" (U+3001, 逗號/逗号 dòu hào) - basically a wide comma. However in Blender we are getting "/、".

When entering text with IME we have to send some keypresses to the IME while others not. If we do not filter them like this we will get duplicated characters. Since D11929: IME Win32: Fix Duplicated Initial Character we do this with IsImeKeyEvent. This patch simply adds forward slash to the list of keypresses to send to IME.