add RequiresHover field to StatefulInteractable

[smarwecki]

Overview

Added a (default false) "RequiresHover" field to StatefulInteractable, of which the only inheritor in the package is PressableButton. Setting this field to true (through inspector or code) prevents basic (also non-MRTK) interactors to trigger a OnClick event when not hovering and ending the selection (on button release, etc.).

Changes

• Added a (default false) "RequiresHover" field to StatefulInteractable, of which the only inheritor in the package is PressableButton.
• Make that field accessible through the editor panel / inspector in Unity.
• Made changes to CanClickOnLastSelectExited method in StatefulInteractable, so that a OnClick event is only invoked when the interactable is being hovered over when RequiresHover field is set.
• Minor bugfix: add isCancelled check as well - when interactors/interactables get unregistered and XRInteractionManager sends a "cancelled" selectexit, the OnClick event is now not triggered.

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[thalbern]

Overall LGTM.
Just for additional info - this change is needed to allow us triggering buttons in mb only if the button is still hovered (eg user presses button down, moves pointer out of interactable - button should not trigger).
@Zee2 / @davidkline-ms do you think this change makes sense or is there another way to get the same behaviour with existing mrtk functionality?

[thalbern]

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[thalbern]

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