Implement plus button on TabBar

[nmichaud]

This PR implements a plus button on the TabBar (similar to google chrome) that will trigger an event when clicked. I've wired up this event for the TabPanel to emit a AddWidgetRequested event, which can be handled by the end user to create the appropriate widget and add it to the panel. A similar approach can also be implemented for the DockPanel if desired.

The CSS is a bit tricky - currently the plus button floats to the end of the TabBar instead of following the tabs.

[ellisonbg]

Woah! I have been talking to folks about this recently. Would be spectacular to see this happen. I will dive into this and begin to review soon.

[ellisonbg]

In the meantime, can you post a screenshot?

[nmichaud]

Here's an example with the DockPanel (not yet part of this PR - I'll push the commits soon)

[nmichaud]

@ellisonbg @jasongrout @afshin It should be ready to review now. I've also updated the dock panel example to expose an additional context menu item when you right-click on the dock panel to toggle the plus button.

[afshin]

I'm happy to look as well.

[nmichaud]

@ellisonbg @afshin Any thoughts on this?

[nmichaud]

Rebased onto master and force pushed

[nmichaud]

Pinging @ellisonbg @jasongrout @afshin again. Any interest in this?

[afshin]

Sorry for leaving you hanging with this PR @nmichaud! I'll commit to reviewing this PR this week! Sorry again for such a long wait!

[nmichaud]

@afshin Sure no problem, just wanted to make sure this was still of interest.

[afshin]

@nmichaud thank you so much for your patience!

I am 👍 on this broadly, I left some API surface area suggestions above.

Could you please push your example updates as well?

[nmichaud]

Thanks for the review @afshin. I've updated with the API changes you proposed.

The dockpanel example has already been updated - right click on the DockPanel to bring up the context menu, and then select the last menu option ('Toggle add button') to see it in action.

[afshin]

The dockpanel example has already been updated - right click on the DockPanel to bring up the context menu, and then select the last menu option ('Toggle add button') to see it in action.

Oops, I got confused by the screenshot 😂

[nmichaud]

The dockpanel example has already been updated - right click on the DockPanel to bring up the context menu, and then select the last menu option ('Toggle add button') to see it in action.

Oops, I got confused by the screenshot 😂

Yeah, apologies I didn't make it obvious in the beginning.

[afshin]

Thanks for this feature and for the patience!