Cross tech snapshots & safari fix

- Cross-tech snapshot restore
- Fix for snapshot restore on Safari where there is some weirdness in how it handles the `currentSrc` attribute on `HTMLMediaElement`.

Safari scenario
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1. videojs-vast-plugin sets src attribute to the preroll media file - the src attribute is updated here.
2. Safari Adblock blocks the media request - the `currentSrc` attribute is not updated if the media request fails.
3. videojs-vast-plugin calls endLinearAdMode, resulting in snapshot restore
4. currentSrc still points to the original content and so matches the content. restore function just calls `player.play` instead of properly restoring the snapshot.

It's an ass of a conditional but I think it will handle all possible scenarios. 

The version bump is for `currentType` support which is required for snapshot restores where the required tech is different from the current loaded tech.