Add IME text rendering

This shows the uncommitted text in a box in the bottom left corner.
This doesn't show the selection (defined by the start and length fields
in the event) yet, but this is already much better than it was on its
own, and I don't know how urgent the selection is since it's broken on
Windows anyway.

desktop_version/CMakeLists.txt

@@ -82,6 +82,7 @@ set(VVV_CXX_SRC
     src/Graphics.cpp
     src/GraphicsResources.cpp
     src/GraphicsUtil.cpp
+    src/IMERender.cpp
     src/Input.cpp
     src/KeyPoll.cpp
     src/Labclass.cpp