add overriding tab bar and allowed splits on a per node and surface basis

[0xcaff]

these changes are made in a backwards compatible way.

i'm looking for feedback on naming, i think it could be more clear. maybe docking override?

also maybe the example could be made a bit more clear? maybe i should move it out of hello or put it behind a flag?

[Adanos020]

I think this design overcomplicates how this library is used because it now has two places where allowed splits are controlled. What I'd do instead is get rid of the AllowedSplits from DockArea and instead make them overrideable from TabViewer only. This way, if someone wants to change the allowed splits for all tabs, they can just return one value from TabViewer::allowed_splits unconditionally.

This would mean:

• getting rid of the AllowedSplitsOverride enum altogether;
• removing DockArea::allowed_splits field and builder functions;
• changing the return value of TabViewer::allowed_splits to Option<AllowedSplits>, where None would represent the current NoDock variant.

Does this sound good?

[0xcaff]

I agree. I avoided this design as it involved making a breaking change. If we're happy to break the API, I'm happy to do things this simpler way.

Also, as posted in discord:

After thinking about it a bit, the concept needs a bit more work. I decided to vendor the dependency for now and make whatever changes to understand what exactly I'm trying to do. Currently, if all the tabs are closed from a pane and the parent node is no dock, it will not be possible to open that pane again. This is kinda a weird UX.

Do we want to proceed with the proposed changes or spend more time figuring out what is ideal?

[Adanos020]

I think we should prioritise usability over backwards compatibility. Especially since we're still in 0.x 😉
NoDock could also be a separate feature, worked on in a different PR if it's a bit of a pain to design properly.