Add Share link section to Share dialog

[ggeisler]

Part of #986.

The Share link section is intended to look something like:

• Add a textfield, populated with the URL of the object's PURL page.
• Add a label "Share link URL" for the textfield, but make it screenreader-only.
• Add a "Copy" outlined button that when selected will copy the URL in the textfield to the user's clipboard.
• Add Facebook and Twitter icons, each which is linked to share the link via those companies' service. See the Share option on a Youtube page as an example. See Add Social Media icons/exports to Share link section ProjectMirador/mirador-share-plugin#5

[jkeck]

@ggeisler / @jvine WRT this task:

Add a label "Share link URL" for the textfield, but make it screenreader-only.

Is putting an aria-label on the <input /> reasonable? That's what MUI example does for the input w/o a visible label.

[jvine]

Huh. I’d have said yes off the bat, but then I found this: https://www.powermapper.com/tests/screen-readers/labelling/input-text-aria-label/

Sigh. Should we be more robust in this one instance, or remain consistent with MUI? Leaning toward the latter I think. Gary?

[ggeisler]

I suspect we might have more than one instance of this in the future (i.e., search panel might have an input with hidden label) but not sure that really helps make a decision. From that web page JV found it looks like the support for the aria-label support is improving and fails in pretty limited cases, so I'd be comfortable sticking with the MUI approach.