[#2135, #2136] Add multi editor to make additional descriptions editable

[arbron]

Creates a new {{multiEditor}} handlebar helper that takes configuration objects (prepared by the {{source}} helper) to display multiple descriptions within a single editor:

Editor.Target.Selection.mov

Also displays the contents of system.description.chat for item chat messages if present to allow for custom chat description.

Resolves #2135
Resolves #2136

[ccjmk]

I'm interested in using this for #1696 once this PR goes through, it would make for a much neater UX/UI imo.

[Fyorl]

I think my only hangup at the moment is that I'm not sold on the UI of selecting a description to edit via a drop-down. In some discussions around this feature it was suggested that a slide-toggle might be nice for most cases where there's only two descriptions to choose from. Something like fa-toggle-on and fa-toggle-off. The problem is that what I think will be perhaps the most-used alternative description is the item unidentified description, which unfortunately has 3 descriptions (normal, unidentified, and chat), so a slide-toggle cannot work, and we would need to fall back to a drop-down.

So first maybe we could consider whether we need the chat description at all? Its use case is fairly obvious but it seems like more of a nice-to-have, rather than a necessary feature. I personally quite like the idea of being able to quickly toggle between identified and unidentified description as a DM, that feels like a nice UX to me.

Alternatively, because I also quite liked what @ccjmk proposed in #1696 with the ability to see all descriptions at once, we could potentially do something like an accordion style UI (maybe using the <details> element or something?)

Having multiple editors in the same tab can be quite awkward to style, so I would propose that we side-step the issue by having the edit button instead pop out a separate editor dialog that is edit-only mode (similar to how journal page editing works.)

Obviously this is entirely subjective so I am not insisting on anything here but am interested to see if we can iterate on this design at all.

[krbz999]

This seems like a use case for tabs.

However, if a pop-out text editor would allow collaboration that is to me 100% the ideal.

[arbron]

@Fyorl Here is a quick prototype of showing all descriptions inline and replacing the whole tab with an editor:

Multiple.Inline.mov

On locked sheets it hides the first header to avoid clutter:

[Fyorl]

@Fyorl Here is a quick prototype of showing all descriptions inline and replacing the whole tab with an editor:

Looks pretty good to me. One minor point of feedback would be to have the edit button always visible so it's more obvious what you need to do in order to edit the description rather than having to hover over it to find out. Otherwise I think we should be good to proceed in this direction.

[arbron]

Closed in favor of a new PR: #2137