Input Method Editor (IME) support for text buttons

Original patch by @random (D765) with some minor work done by @campbell
and me.

At this place, I'd like call out a number of people who were involved and
deserve a big "Thank you!":
* At the first place @randon who developed and submitted the patch
* The Blendercn community which helped a lot with testing - espacially
* @yuzukyo, @leon_cheung and @kjym3
* @campbellbarton, @mont29 and @sergey for their help and advises during
* review
* @ton who realized the importance of this early on and asked me for
* reviewing

We are still not finished, as this is only the first part of the
implementaion, but there's more to come!

intern/ghost/CMakeLists.txt

@@ -280,6 +280,16 @@ elseif(WIN32)
 		)
 	endif()
 
+	if(WITH_INPUT_IME)
+		add_definitions(-DWITH_INPUT_IME)
+
+		list(APPEND SRC
+			intern/GHOST_ImeWin32.cpp
+
+			intern/GHOST_ImeWin32.h
+		)
+	endif()
+
 	if(WITH_INPUT_NDOF)
 		list(APPEND SRC
 			intern/GHOST_NDOFManagerWin32.cpp