Make Gap duration adjustable

[Cmdv]

Description:

This pull requests fixes #69

Make sure to describe (where applicable):

• The ability to adjust the gap duration in the sidebar

Checklist:

Please make sure to check the following items (that are applicable.)

• Doesn't duplicate any existing PR
• Automated tests added
• Includes relevant user guide/documentation changes

How to test:
add video gap, select gap and on the sidebar adjust it's duration.

TODO: Testing instructions for reviewer.

[Cmdv]

I managed to get an element added and it displays the correct duration length of the gap. But when I edit nothing update, wondered if I could have some pointers as to how I would adjust the duration of the gap?

I tried to copy clipSpanControl but it looks like it uses VideoAsset which is on the type but this is non existent on VideoGap, does this have something to do with it?

*edit: looks like it would live in here?

komposition/src/Komposition/Application/TimelineMode.hs

Lines 190 to 196 in f4db3f0

	FocusedClipStartSet start ->
	model
	& modifyFocusedVideoPart (\case
	VideoClip ann asset ts speed ->
	VideoClip ann asset ts { spanStart = start } speed
	vg@VideoGap{} -> vg)
	& refreshPreviewAndContinue gui

[Cmdv]

sorry rubber ducking here 🦆
Got the VideoGap state to update so this all works just need to do this to audio gap to then tests 😄

[Cmdv]

Just took another look at this and noticed that "start end" is implemented for the audio as of yet so I won't be able to add this feature to audio gap without implementing that first.

I also can't seem to find a test case where this would live 🤷‍♀️

[owickstrom]

OK, so this would need to use the new undo/redo machinery now, but there are examples already (setting duration of a clip). Would you mind rebasing the PR and implementing it in UndoableAction? Totally get if you don't, I can move it otherwise.

[Cmdv]

yeah not a problem will take a look this evening, I assume the new functionality came in this PR #82 ?

[owickstrom]

@Cmdv that's right 👍