Improve view of long signatures

[pikinier20]

This problem is with us since change of members view:

As you can see when member has long prefix (e.g. sealed abstract modifier) then it hides to the left.

[dylemma]

I also noticed this while I was fiddling with color theme stuff. It seems to me like the simplest solution is to give up on presenting the signatures like a "table" (i.e. trying to make the word def line up with each signature), though maybe there's some opposition do doing so. Another little annoyance is how the keywords hide behind the 🔗 icon. Here's a little preview of some changes I have in my working copy, LMK what you think:

A potential alternative is showing those keywords above the main signature, like how you do with annotations in an expanded signature:

although I'm not sure I'm a fan of that.

[pikinier20]

TBH I like the table appearance because lined up member names makes whole documentation very clear. However, the second option might look very bad with annotations being above modifiers so I'm also not a big fan. I thought about hiding modifiers at first glance and show them after click (clicked signature would look like your first version - without lineup) but I'm not really sure if this information can be hidden (maybe it's useful to somebody).

[bishabosha]

it looks like for scala 2 the margin is just a lot longer, but they do also skip override flag (implied by Definition Classes entry) and annotations do not show until you expand

[pikinier20]

I think it's fixed with #13317