qt/qml: SMPTE Timecode integration

This was actually meant to be added a while ago, but it had to wait until the toolbar control handling refactor.

It uses the smpte timer api that was added to the backend (player) two years ago.

I tried to follow the same approach that was used for player timer integration.

@tguillem, if you want and if you have time you can also make a quick review as afaik it is based on your work :)

Related: #22818 (closed), #16105 (closed).