TTP# 340272 - IME crash when typing Korean in the Description TextBlock of SSourceControlSubmitWidget
- FWindowsTextInputMethodSystem::Initialize now checks if an IME is active when it's called, and will update the active IME state appropriately.
- Changed TSF to use AssociateFocus rather than SetFocus to fix some issues where the IME would become active incorrectly when the window focus was changed.
- Some belt-and-braces fixes for the IMM based code path (which was what was showing the crash, even though a TSF based IME was active).
#codereview Saul.Abreu, Max.Preussner
[CL 2251530 by Jamie Dale in Main branch]