(FR) Set _AbsoluteTime frame props

[YomikoR]

As suggested by the API reference: https://amusementclub.github.io/doc/apireference.html#reserved-frame-properties

[AkarinVS]

What's the intended use case? Unlike relative frame duration props, absolute time properties can be easily out of date: I'm not aware of any temporal filters that update it. e.g. a single Trim can invalidate all _AbsoluteTime properties.

[YomikoR]

For telling users where to trim source audio, for example. A Trim call means you manage your clip by frames.