Fix popup and tooltip positioning when not fitting in the screen. Amend fa42ccea8.

# Conflicts:
#	docs/CHANGELOG.txt

docs/CHANGELOG.txt

@@ -68,6 +68,8 @@ Other Changes:
   tabs reordered in the tab list popup. [@Xipiryon]
 - Columns: Fix inverted ClipRect being passed to renderer when using certain primitives inside of
   a fully clipped column. (#3475) [@szreder]
+- Popups, Tooltips: Fix edge cases issues with positionning popups and tooltips when they are larger than
+  viewport on either or both axises. [@Rokups]
 - Metrics: Various tweaks, listing windows front-to-back, greying inactive items when possible.
 - Demo: Add simple InputText() callbacks demo (aside from the more elaborate ones in 'Examples->Console').
 - Backends: OpenGL3: Fix to avoid compiling/calling glBindSampler() on ES or pre 3.3 contexts which have 

docs/TODO.txt

@@ -219,7 +219,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - popups/modals: although it is sometimes convenient that popups/modals lifetime is owned by imgui, we could also a bool-owned-by-user api as long as Begin() return value testing is enforced.
 
  - tooltip: drag and drop with tooltip near monitor edges lose/changes its last direction instead of locking one. The drag and drop tooltip should always follow without changing direction.
- - tooltip: tooltip that doesn't fit in entire screen seems to lose their "last preferred direction" and may teleport when moving mouse.
  - tooltip: allow to set the width of a tooltip to allow TextWrapped() etc. while keeping the height automatic.
  - tooltip: tooltips with delay timers? or general timer policy? (instantaneous vs timed): IsItemHovered() with timer + implicit aabb-id for items with no ID. (#1485)
  - tooltip: drag tooltip hovering over source widget with IsItemHovered/SetTooltip flickers.