imgui really hates it when we update the modifier key state after igNewFrame.
The result is:
void ImGui::ErrorCheckEndFrameSanityChecks(): Assertion
`(key_mod_flags == 0 || g.IO.KeyMods == key_mod_flags) &&
"Mismatching io.KeyCtrl/io.KeyShift/io.KeyAlt/io.KeySuper vs io.KeyMods"'
failed.
Therefore, we buffer the modifier state information and update it in the IO
object right before we call igNewFrame.