prevent double nesting using gesture

[adumesny]

Description

• remaining fix for Dragging widget into parent grid and nested child grid #992 to prevent a nested grid from going inside another until we can do the right thing down the line. Very broken otherwise
• also fixed heuristics to work like regular items (ignore enter/leave for sub grid dragging)

Checklist

• Created tests which fail without the change (if possible)
• All tests passing (yarn test)
• Extended the README / documentation, if necessary