Add better variations for Separator block

[mtias]

The current variations of the separator are a bit limiting and not super ergonomic. We should see about:

• Allowing changing the width of the line.
• Allow changing the color.
• Improve the circles or offer size controls (can apply to circles and lines).
• Offer other shapes (like zig-zag cc @jasmussen).
• Consider also adding the Spacer block mechanics to give space before/after.

[richtabor]

For reference, here's how we've adding spacing mechanics to our separator block within CoBlocks, essentially merging the Spacer and Separator blocks:

[jasmussen]

Nice. The zig-zag shape being referred to is shown in this lovely ticket, which also supports the idea of a disparate blocks for separator designs and top/bottom group blocks shapes. From that comment, here are some of the more "out there" ideas that nonetheless support the idea of changing dimensions and colors:

Here are more basic ones that could simply be inline SVGs, which would let you easily configure the stroke-widths or colors:

[senadir]

this PR #16784 should handle the case of adding colors, I will follow up with other PR handling other points.

I prefer to to handle each point in a PR for it to be easy to test & review

[senadir]

this PR #16925 handles the case of width changing, it would have added alignment support if not for some problems in floating.

next PR will handle this

Improve the circles or offer size controls (can apply to circles and lines)

[paaljoachim]

I went ahead and added two new issues:
Adding styles such as waves, jagged and loops.
#25991

Controlling the height of the Separator block.
#25989

[ricjcs]

The default line is supposed to be a short line.

However, some themes like Twenty Twenty-One, the default line is different and there is no short line.

It should be possible to always select the short line, regardless of thema's default line.

[caseymilne]

Can we make something with a dashicon icon like ----------- icon --------------- with some alignment options for icon placement like:

---- icon -------------------------------
---------------------------- icon -------

[tanjoymor]

Nice to see this was being looked into. Would love to see it implemented. The Separator and Dynamic blocks are super limited at the moment.

[annezazu]

Noting this related issue for a new shape divider block: #16351