Nav block - conditionally display first horizontal rule if empty placeholder

[getdave]

In #37884 (comment) @spacedmonkey noted that lower permission users can end up with an empty placeholder. He was concerned about the <hr /> to the right of the block name.

I wonder whether in such circumstances it might be confusing to the user to see an empty block. Should we communicate somehow that this is an expected state due to their permissions and not an error? Some kind of inline message? Open to suggestions.

Would appreciate design input here so pinging @javierarce and @jasmussen who have worked a lot on the block.

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This PR looks good. It is a nicpic, not sure it should be part of this PR. But the is a random line here after navigation.

Otherwise this PR looks good.

Originally posted by @spacedmonkey in #37884 (comment)

[javierarce]

I wonder whether in such circumstances it might be confusing to the user to see an empty block. Should we communicate somehow that this is an expected state due to their permissions and not an error? Some kind of inline message? Open to suggestions.

If I recall correctly a snackbar appears when the user clicks the menu or tries to change it, so I don't think we need to add more text (also, the menu could contain items, and inserting a message could be confusing).

I like the idea to make the disabled nature of the menu more prominent. I think we could add a gray background and lower the opacity of the content. Hiding the line would be nice too.

Here's a proposal:

[scruffian]

The experience now is different, but not better!