Feature/979 copy field values

[i-just]

Description

On the entry/category edit page (elements that support autosaving drafts):

• implemented a new button that allows you to copy all translatable field values from the selected site;
• translatable field icon now triggers a HUD, which contains a form that allows you to copy just that field’s value from the selected site;
• copy action is applied to the top-level fields (e.g. entire matrix field)
• plugins need to implement CopyableFieldInterface to use this feature

TODO:

• switch the sites selector in the copy form (in the hud) to a disclosure menu

IMPORTANT: once this feature is released, an update to craftcms/html-field needs to be released; PR 6

Related issues

DEV-979

[i-just]

@brandonkelly as per our chat yesterday, 4.5 is merged into this, conflicts resolved (not many) and tested that it still works like it did in December. Please LMK if you have any questions or if it still doesn’t want to work for you.

[benjamindavid]

I’m sorry if these things have already been discussed or ruled out, but here’s some feedback on this:

• Explain somewhere that only translatable fields will be copied.
• If there’s no translatable fields, or if copying won’t change anything, the copy button could be disabled or invisible
• Add a blue flash for fields that have been copied and currently visible
• The top area of the page is already a bit crowded with buttons, maybe we could try to find a shorter label for the copy button. Longer term we could clean up that UI with a three dot menu or something like that?

[i-just]

Targeting the 5.0 branch now.
I’m putting it back into draft to work on minor compatibility changes & to test.

[brianjhanson]

Closing in favor of #14056