Add an extension menu with custom actions

[tvanlaerhoven]

Add an extension menu to the UI that enables to easily add custom actions.

For example:

  <ExtensionMenuButton>
    <ExtensionButton label={'Schedule ad'} onPress={() => {
      player.ads.schedule({
        integration: AdIntegrationKind.google_ima,
        timeOffset: 1e-3 * (player?.currentTime ?? 0) + 3, // in 3 seconds from now
        sources: {
          src: 'https://cdn.theoplayer.com/demos/ads/vast/dfp-preroll-no-skip.xml',
        },
      });
    }} />
  </ExtensionMenuButton>

The menu is hidden if no custom actions are defined (default).