Viewports: Todos, Tooltips/menus not automatically forced into their own viewport when the NoMerge flag is set (however the multiplication of viewports makes them more likely to protude and create their own). Win32: try to make primary monitor the first tin the list. (#1542)

TODO.txt

@@ -258,6 +258,14 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - focus: SetKeyboardFocusHere() on with >= 0 offset could be done on same frame (else latch and modulate on beginning of next frame)
  - focus: unable to use SetKeyboardFocusHere() on clipped widgets. (#787)
 
+ - viewport: popup/tooltip glitches when appearing near the monitor limits (e.g. opening a menu).
+ - viewport: clamp windows position within monitors (especially important on monitor configuration change) -> clamp to closest rectangle.
+ - viewport: platform: introduce getfocus/setfocus api, so e.g. focus flags can be honored, imgui-side ctrl-tab can focus os window, OS alt-tab can focus imgui window etc.
+ - viewport: store per-viewport/monitor DPI in .ini file so an application reload or main window changing DPI on reload can be properly patched for.
+ - viewport: IME positioning are wrong.
+ - viewport: vulkan renderer implementation. 
+ - viewport: need to clarify how to use GetMousePos() from a user point of view.
+
  - inputs: we need an explicit flag about whether the imgui window is focused, to be able to distinguish focused key releases vs alt-tabbing all release behaviors.
  - inputs: rework IO system to be able to pass actual ordered/timestamped events. use an event queue? (~#335, #71)
  - inputs: support track pad style scrolling & slider edit.