ktooltipwidget: Fix tooltip positioning

Summary:
Partially fix [[ https://bugs.kde.org/show_bug.cgi?id=388583 | Bug 388583 ]]
Display tooltip at correct position in dolphin when
  - Tooltip is displayed above file item, or
  - Content width exceeds screen width

CCBUG: 388583

Test Plan:
Visual inspection specially for equal distance to file item (3px)
Patch applied:
{F5662669}

Currently partial display:
{F5662680}
Patch applied:
{F5662688}

Currently invisible tooltip (displayed off-screen).
Patch applied:
{F5662675}

Reviewers: elvisangelaccio, ngraham

Reviewed By: elvisangelaccio

Subscribers: #frameworks, dfaure, cfeck

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D9973