References T49862
Currently if you add a Scene to the VSE, and then adjust the start or end frames of the scene, the contents of the strip in the VSE is not updated (e.g. if you have made the scene longer, you cannot access the new frames in the scene strip). Adding the scene again would give a different result.
This patch finds any VSE strips referencing the modified scene and adjusts the source length and end still / offset values to produce a result that is the same as if you added the scene to the VSE after making the change, with the exception that it does not change the length of the scene strip itself (because it might bump into nearby strips and be forced onto another channel).
To get exactly the same strip as adding again from scratch, the user will have to drag the end marker to suit, but this is simple because the VSE will show an updated green area representing the source scene's range.
Simple demo here:
https://www.youtube.com/watch?v=08ovpPVXatY