[NEEDS-DOCS] [Layer Properties dialog] Move Legend tab contents to Rendering tab

[DelazJ]

and set the groups collapsible
The number of tabs in Vector layer properties is increasing. This PR moves the Legend tab (containing a single tool to interact with layer tree - hence layer rendering?) into the Rendering tab.
also make groups collapsible for convenience

I also wonder if there's a way to merge parts of "Information + Metadata + Source" in less tabs. They are all somehow about metadata and while i agree that metadata are important things, 3 tabs on top of the dialog may look too much.

[nirvn]

-1, legend widgets aren't restricted to impacting rendering.

[nyalldawson]

Yep, -1 here also. I'd never look under "rendering" tab for legend related settings.

[borysiasty]

As stated above, I wouldn't mix rendering and GUI interactions. However, in general +1 for merging that tab somewhere. The same with Display (and the metadata stuff you mentioned). If we can't find the right places, we need to think what new features we could implement to fill these empty tabs! 💪

[Gustry]

Maybe I can move the Information tab to the first tab in the Metadata one? But I'm wondering about the behaviour when we will want to save/load metadata from with QEP 91, if we want to update the Information tab.

[nyalldawson]

@DelazJ ok to close?

[DelazJ]

@Gustry I also thought about putting Information inside Metadata but I'm not sure it would be a nice UX: a read-only tab among a lot of "forms to fill" tabs. Maybe moving down Metadata in the list (I propose a new organization of the dialog at qgis/qgis3_UIX_discussion#51)
@nyalldawson Yes we can close. There seems to be a consensus against.