Move CommunalSwipeDetector to SystemUI/src/.../communal/

This CL moves CommunalSwipeDetector to the SystemUI/src/ directory,
closer to other communal specific sources. This file was introduced by
mistake in the STL library in ag/27499252 and moved (but still kept in
the STL library) in ag/28220116.

Bug: 375119446
Test: N/A pure move
Flag: EXEMPT pure move
Change-Id: I808715dd3bf2b2cf52db12f072c99eaef7778d78