Check for gesture zone in TraceGesture too

[snqb]

Fixes #2605

Turns out, the problem is not Android-only, it's also reproducible for iOS, see the video attached.
(android video is in the original issue)

IMG_0968.MP4

Thing is, we have the notion of scroll vs gesture zone in the MultiGesture, while we don't track it in TraceGesture, thus leading to half-painted canceled traces. Surely, it doesn't affect functionality, but is kinda misleading, since we have this strong separation of scroll vs gesture zones.
This PR moves out the gesture zone logic to a util file, and reuses it in both MultiGesture and TraceGesture to share the logic.

[raineorshine]

Great, this makes a lot of sense now that we see it is not Android-specific.

Nice troubleshooting and factoring out the shared functionality.

Thank you!