Add configurable background interaction mode to allow forwarding touches to presenting view

[rahulVermaSimpplr]

This PR integrates changes from slackhq/PanModal#115 into this fork, introducing a backgroundInteraction property on PanModalPresentable and the PanModalBackgroundInteraction enum.
With these changes, developers can control how touches on the dimmed background are handled:

.dismiss — dismiss the modal (existing behavior)
.forward — forward the touch events (including taps, scrolls, and drags) to the presenting view’s hierarchy
.none — swallow the touch without action
This enables scenarios where the bottom sheet remains interactive and the presenting view can also receive gestures on the uncovered background area (e.g., scrolling lists, interacting with buttons).
No breaking changes — existing behavior remains the default unless backgroundInteraction is overridden.

[salesforce-cla]

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[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @ilia3546 to sign the Salesforce Inc. Contributor License Agreement.