No Indication that Panel Body cannot be collapsed

[milesdelliott]

Describe the bug
The Panel Body component accepts an opened prop which if passed will force the panel open. When the panel is forced open there is no indication that the panel cannot be collapsed( visually or in the code)

Expected behavior
I think at a minimum the arrow should be hidden, and maybe a disabled state on the button, or rendering a different element other than button. I'm not sure what other indications should be there

I have a branch ready to remove the arrow icon, but I figured I would open this issue to get feedback on what more should be done.

Screenshots
This Panel cannot be collapsed

This panel can be collapsed

Additional context
Using Gutenberg version 3.8

[karmatosed]

I would say the arrow should be hidden if it can't be collapsed, there seems no point in showing the arrow if that is the case.

[rodrigoi]

I think I'll close this since it'sa duplicate of #9522 .