Reland keeping selection of widget at the end of dragging

Previously, the Glanceable Hub clears widget selection as soon as a
widget dragging starts. This change makes it so that a drag action also
selects that widget being dragged, and does not reset it after the
dragging completes.

The previous change was reverted due to a regression that the widget
resize outline shows during dragging which appears above the dragging
widget. This change has fixed that.

Test: atest CommunalEditModeViewModelTest
Test: verified selection remains at the end of a widget dragging;
      see bug for before and after video
Test: verified outline does not show above the dragging widget; see
      video
Fix: 376492600
Flag: com.android.systemui.communal_hub
Change-Id: I2c6159daea53947674ccaf6ccab4e570c60cff3d