Stick focused object tooltip to slightly above its top (#4710)

Fixes #4710 (closed)

makes openmw playable

ship 1.0 NOW

This fixes focused object tooltip position calculation and brings some peace to the remnants of my soul after 6 years. getScreenBounds handles bounding boxes that go partially offscreen very poorly (it doesn't do perspective correction, doesn't check near plane intersections, tries to use offscreen corners, etc. etc.). Morrowind avoids that problem altogether by only computing the coordinates of the topmost point and falling back to the top of the screen if it's unavailable. It also applies a vertical offset to the computed vertical coordinate. So do that. Note the tooltip is currently always centered horizontally.