Can't distinguish between seek to time X and stop, versus seek to X and play

[azaroth42]

Content-State assumes that the time point is the beginning of the time to start playing from.
However the user might want to seek to that point in time and NOT start playing.

Proposal add a new behavior to autoplay vs not -- e.g. go to start of a range of time and DONT play

Example from 3d: want to seek in a temporal model to a point in time but then stop time and let the user move the camera around a bit and then maybe hit play.

Related to temporal fragment issue of instant vs t.

could live on: collection, manifest, range, canvas, scene, annotation

(e.g. captions in long list of annotations, click on a particular timed caption, client seeks to the beginning of the duration of the annotation and then either starts playing or not)

Default is not autoplay.

Also need no-autoplay to be able to override autoplay, e.g. in content-state 2.0

[azaroth42]

Related to #2280 & #2271