Add horizontal line to problem hover

[weinand]

testing #69204:

I suggest to separate the hover's status bar with the Peek Problem and Quick Fixes actions from the "contents area" by another horizontal line:

[weinand]

And please consider to use a smaller font for the hovwer's status bar (or better: the same size as the main status bar).

[sandy081]

@weinand This is how it looks if we use same style as status bar

Does not it look odd with the rest of the hover?

[sandy081]

I think it looks good after adding a default status bar background

[bpasero]

@sandy081 I like it a lot. should "Quick Fix" appear first though?

[sandy081]

Done