Fixes#8406
Spatial split navigation now wraps at the edges.
We first attempt the nearest spatial target using the existing slot geometry.
If there is no candidate in the requested direction, we synthesize a wrapped
target by shifting the current slot by one full grid in the opposite
direction and reuse the same nearest-distance logic.
This fake target works because the grid is 1x1, so by moving it a full
grid size in the opposite direction, we effectively wrap around to the
other side of the grid.
969748eb35