Use new Icon API for Tabledrag multi-arrow icons

[quicksketch]

Now that we have the new SVG icons from #364, we should use one for tabledrag:

[quicksketch]

Work-in-progress PR filed at backdrop/backdrop#4720

Although not strictly necessary, I added tabledrag.js to a library so it can be added (along with its icons) via backdrop_add_library() instead of backdrop_add_js(). I also moved its CSS outside of system.css, since it is not needed on most pages.

[indigoxela]

I added tabledrag.js to a library ... I also moved its CSS outside of system.css

Ouch, that doesn't sound like it's a backwards compatible move, though. At least one of my contrib modules and probably most of my themes will be affected by such a change. 😬

[argiepiano]

Ouch, that doesn't sound like it's a backwards compatible move, though.

AFAIK you can still load tabledrag.js the "old" way with backdrop_add_js, despite it being added to a library, no? If not, several of my custom modules will also be affected...

[quicksketch]

@indigoxela Yeah... I wonder if this is feasible as well; moving tabledrag CSS into its own file. Are you actually overriding system.css (not system.theme.css)? That's a big set of functional CSS to override.

@argiepiano From what I've seen in contrib modules, it's pretty unusual to add tabledrag.js directly, usually you call backdrop_add_tabledrag(), which is needed to add the corresponding settings to the page. That in turn adds the JS (or the new library in this case).

[indigoxela]

Are you actually overriding system.css (not system.theme.css)?

I'm overriding tabledrag styles in (almost?) every theme I create. Just CSS. But moving things around sounds really dangerous re backwards compatibility. Needs proper testing, as tabledrag's used in lots of module and probably CSS gets overridden in many (most) themes. Contrib or custom.

... usually you call backdrop_add_tabledrag()

Yes, that's what my module uses.

However, tabledrag is one of those things used in lots of modules. So my "bc alarm" got triggered. 😉

[klonos]

With regards to the icons:

• consider increasing the contrast, as that light gray over white background seems insufficient (haven't actually tested though)
• perhaps also use arrow-elbow-down-left/arrow-elbow-down-right icons from the Phosphor icon set instead of the custom tree.png and tree-bottom.png ones we currently use: