Drive ImeTextInput with injected SDL events and an injected clipboard
provider, no window and no real input method: text editing events become
the shown preedit and a commit ends it; Ctrl+V, Shift+Insert and
Ctrl+Shift+V paste while a dialog or session captures the keyboard;
repeats, Alt, other modifiers, key releases, other windows and Ctrl+C,
Ctrl+X read nothing; nothing reads the clipboard while no dialog captures
the keyboard or no provider is installed; a clipboard of megabytes stops
at the dialog limit.
