Propagate navigation events up in hierarchy in InputSystemUIInputModule

[f1yingbanana]

Description

Imagine a panel containing a single selected button, where pressing the escape key should dismiss the panel. The most intuitive way to implement this is to wire up the escape key with a cancel event in the EventSystem. Button, which is the currently selected object, doesn't implement ICancelHandler, so naturally it should let another UI element higher up in the hierarchy, a script attached to the panel, do the work.

This currently doesn't happen, as the event is not propagated up the hierarchy. This PR adds an option (default false for compatibility) to surface IMoveHandler, ISubmitHandler and ICancelHandler up the hierarchy for a custom UI element to handle them.

Changes made

Added a new flag propagateNavigationEvents to InputSystemUIInputModule, so that when the flag is true, IMoveHandler, ISubmitHandler and ICancelHandler are invoked with ExecuteHierarchy instead of a simple Execute.

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:white_check_mark: f1yingbanana
:x: Jiacong Xu

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[Rene-Damm]

Thanks for the contribution. Looks like a good change to me. Raised it internally in team.