Implement Tabs node minimum size

[groud]

Fixes a long overdue 😛 TODO in the Tabs node.

This allow with the new "clip_tabs" property to set up a minimum size to the Tabs node. It's enabled by default to keep compatibility.

Also, I changed the logic a little bit used to choose when a tab should be shown or not. Previously, it always removed the size of the increment and decrement buttons from the available space, even if the last tab would fit in the parent's size. So now, it instead waits for the last bit of space available to show the buttons. (Not sure if there was an issue about that, but didn't find one)

To illustrate the changes:

Peek.30-03-2021.12-28.mp4

Bugsquad edit: This closes #31238.

[groud]

I had to add few other changes, to make sure the 2nd change in the PR (showing buttons only when needed) works properly.
For now I could not find any issues, it seems to work fine.

[KoBeWi]

clip_tabs property needs doc description, everything else looks ok.

[groud]

Done, I added the documentation.

[akien-mga]

Thanks!