tst_QScroller::overshoot was initially a boilerplate, making it
difficult to understand what was actually being tested.
Refactor this test to be data-driven. Additionally, create a new test
function, overshoot_segments, which was part of
tst_QScroller::overshoot and should be tested independently.
Transfer the blacklisted platform of overshoot to overshoot_segments.
Change-Id: I59d89dfab4bb09c41fce99ad4f40163736c6ef78
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>