Remove Modifier.handleDPadKeyEvents from pillarbox-ui

[MGaetan89]

Pull request

Description

This PR removes Modifier.handleDPadKeyEvents from pillarbox-ui. Instead, we now have a dedicated private extension where needed (ie. in DelayedVisibilityState.kt), and a new extension in pillarbox-demo-tv.

Changes made

• Remove Modifier.handleDPadKeyEvents from pillarbox-ui
• Create Modifier.onDpadEvent in pillarbox-demo-tv
• Replace all usages of Modifier.handleDPadKeyEvents and Modifier.onPreviewKeyEvent in pillarbox-demo-tv with Modifier.onDpadEvent
• Fix Modifier.toggleable in DelayedVisibilityState to not break the Modifier chain

Checklist

• Your branch has been rebased onto the main branch.
• APIs have been properly documented (if relevant).
• The documentation has been updated (if relevant).
• New unit tests have been written (if relevant).
• The demo has been updated (if relevant).
• All pull request status checks pass.