✨ Add more SkyLight APIs for improved window/screen selection

[MrKai77]

Adds two private SkyLight APIs: SLSCopyBestManagedDisplayForPoint and SLSFindWindowByGeometry.

SLSCopyBestManagedDisplayForPoint
Picks the display at a given point using the system's own selection logic instead of our manual bounds iteration. Not really a performance win, but the value is that we match WindowServer's tie-breaking at boundaries, so we can't drift from it (in practice the two seem to agree, though matching the source-of-truth is cheap insurance). Falls back to the old iteration if the symbol fails to load.

SLSFindWindowByGeometry
Finds the window at the mouse position. Previously we'd ask AX for the UI element under the cursor, or fall back to walking CGWindowListCopyWindowInfo and taking the first frame that contained the point. The fallback was unreliable, as it could skip the frontmost window and return one obscured beneath the actual target. SkyLight's geometry hit-test gives us the right window directly. If this symbol is unavailable, we still fall back to the old system.

[SenpaiHunters]

We're missing any error checking for SLSFindWindowByGeometry as you're doing

_ = SLSFindWindowByGeometry(cid, 0, 1, 0, &screenPoint, &windowPoint, &hitWindowID, &windowCID)
return hitWindowID != 0 ? hitWindowID : nil

If we ignore errors, that's acceptable. I'm uncertain about what it would return; if it yields nothing useful, we can disregard it. Additionally, I see no changes or updates needed. If we don't need to log the SLS failure, it's ready to commit.