Handle font licenses when editing theme metadata

[matiasbenedetto]

What

• Handle font licenses in the frontend 'edit theme metadata'.
• Adds a button to get theme fonts license text info updated.

Why?

To avoid the need of collecting the font licesing information manually.

• This is part of the effort to re-introduce the font license theme automation (
  Font licenses are no longer automated with new Core Font Library functionality Font licenses are no longer automated with new Core Font Library functionality #525).

How

Calls the /font-families/ endpoint and process the data to create the fille the font credits text area.
Using a button to get the latest licenses has 2 benefits:

• Font assets metadata are loaded only when it is necessary.
• The theme author can add extra text to the one auto generated.

⚠️ This PR depends on #648 being merged

Screencast

This video features how the font licences can be updated for a theme.

Screencast.from.30-05-24.12.00.58.webm

[vcanales]

I see there are a few console.error calls; I think we should implement proper error management instead.

[matiasbenedetto]

I removed the error handling where it was not needed and added it in the function where the license text is requested. If getting the license fails, the UI will throw an alert.

Until merging #648 this PR will display this error:

Screencast.from.23-05-24.12.20.13.webm

Why an alert? Because the snackbar is behind the modal component and is not visible. As that problem is not easy to fix (reference: WordPress/gutenberg#52609) I think for now the alert is good enough.

Screencast.from.23-05-24.12.02.53.webm

[vcanales]

Looking good, although you'll probably have to update the branch with trunk, since there's a new eslint rule enforcing the specification of which rule is being disabled when eslint-disable comments are used.