Apply new structure in the section that shows the comments icon together
with the number of comments so that it is easier to unify them into one
component.
Please note that we updated the comment-number class to comments-count
in order to simplify the css in the new component in the next commit.
Now that comments and TOC can be closed at the same time, we use a flex
layout so the main content uses the available width.
We're also making the comments work better on medium-sized screens,
since previously they had a fixed width and now the width is adapted to
the size of the screen.
Since now the comment box element has a relative position instead of an
absolute one, we need to consider the draft panel height when
calculating the comment box position.
We were using JavaScript to show/hide the Table of Contents.
In my humble opinion, the <details> tag has a few shortcomings [1][2],
which means we should be careful about when to use it.
IMHO a Table of Contents is a good candidate for this tag because it's a
very common pattern to add a show/hide behavior for it, even if using it
means the "navigation" role (which we are *not* using anyway) wouldn't
be identified correctly.
I'm adding a <details> tag to the comments section as well for
consistency and in order to simplify the code. I'm not sure this is as
good an application of the <details> tag, though, but then again I'm not
sure about the interface we use to show/hide the comments (and this
feeling is increased by the fact that we use a different interface on
small screens). If we decide to change the interface in the future, we
might consider using the <details> tag for the Table of Contents but not
for the comments.
Since the <details> tag is not supported on Internet Explorer, I'm
only adding styles to this tag using the `:not([open])` option. On
Internet Explorer <details> will always be opened and so these styles
will be ignored.
[1] https://adrianroselli.com/2019/04/details-summary-are-not-insert-control-here.html
[2] https://daverupert.com/2019/12/why-details-is-not-an-accordion/
