Make JSON inspector editable

[timlehr]

Feature suggestion
Currently the JSON editor is read-only. Making it editable would let us explore & understand how changes affect the composition.

[vfleuryrodeofx]

I'll try and take a look at this feature for Dev days :)

[vfleuryrodeofx]

Hey !
Just a quick follow-up to mention that I took a look at that but unfortunately I think it was beyond my C++ abilities.
I managed to get the editor to be editable by modifying this line https://github.com/OpenTimelineIO/raven/blob/main/inspector.cpp#L75
But I did not go further than that to hook modifications made in the editor to reflect in the current loaded timeline.
If anyone else want to take it up, go for it !

[jminor]

Thanks for giving it a try @vfleuryrodeofx !

A note for anyone else attempting this in the future: I suspect this feature would require noticing edits to the text via some callback in the text editor widget, then deleting the selected item and replacing it with a freshly deserialized object from the edited JSON text. It would also need to be defensive about invalid JSON introduced by typos.