Draft: autotests: Fix QuickTilingTest

AbstractClient::geometryRestore() is no longer initialized when the window is mapped so XdgToplevelClient can send a configure event with 0x0 size if user tries to restore initially maximized window.

However, it broke AbstractClient::setQuickTileMode().

This change intends to fix it (and relevant test) by making maximize quick tile mode compute geometry restore.

If user has dragged the window to a screen edge in order to maximize it, geometryRestore() will be set to the geometry that the window had when user started moving it; otherwise use the current geometry.

It would be nice to unify quick tile mode with maximize mode so the code looks less like spaghetti and less error-prone, but it's out of the scope of this MR.