feat(youtube): add toggle method

[natemoo-re]

Adds @Method() toggle to the <deckgo-slide-youtube> component, which alternates between play and pause states.

TODO: post a message from the YouTube iFrame when the video is played/paused, so that <deckgo-slide-youtube> keeps an internal @State() isPlaying in sync with the video. Currently this implementation only works if play, pause, or toggle are called programmatically.

[peterpeterparker]

Cool idea and thx for the PR @natemoo-re 👍

After merge I allowed my self to remove the @State() decorator on the state variable as it do not need to trigger a new repaint and also make the playPauseVideo a bit simpler I think (no use of typeof, 2dd98ec)

I also added the new method to the DeckDeckGo docs (not yet published, https://github.com/deckgo/deckdeckgo-docs/commit/84af7e780833a0e7e64cb4ed349752154072e5db)