Implement QTest::qEnsurePositionTopLeft() to set and ensure window's position to the left corner

Implement QTest::qEnsurePositionTopLeft() to set and ensure the window's position to the left corner of the screen.

Many cases of flakiness observed on Opensuse are due to un-updated position and frameposition of a window. This flakiness can be fixed by assigning a fixed position and verifying that the window's position corresponds to it.

The helper test function first sets a position using the available top-left corner of the screen and then verifies that the position and framePosition have been updated.

List of flaky tests where that function could have been used/could be used:

• Opensuse

QTBUG-134704 tst_QQuickOverlay::pressedAndReleased is flaky on opensuse - Qt Bug Tracker (not fixed yet)

Set flag FramelessWindowHint to tst_mouseAreaInterop::createView (631693) · Gerrit Code Review (would fixed, not merged)

Set fix position tst_QQuickHoverHandler::window to fix flakiness (629861) · Gerrit Code Review () (would fixed, not merged)

Harden tst_QWindow::framePositioningStableAfterDestroy() (614384) · Gerrit Code Review (would fixed, already merged)

Set window position to fix tst_TapHandler::longPress flakiness (616093) · Gerrit Code Review (would fixed, already merged)

It would be pertinent to add this function to other test functions, but these are meant to be examples where it would fix the flakiness by adding only QTest::qEnsurePositionTopLeft() instead of several lines that are being repeated in the different functions.