Font Library: Improve 'No fonts installed' state when fonts are installed but not activated

[afercia]

Description

Splitting this out from #63211 (comment)

Cc @matiasbenedetto

WHen there are fonts installed but none of them is activated, the UI still refers to a 'no fonts installed' verbiaage:

• Th Styles panel shows a 'No fonts installed.` text,
• The button that opens the modal dialog text is 'Add fonts'.
• The button to open the modal dialog brings users to the 'Upload' tab. It would be best to bring users to the 'Library' tab.

This UI could be improved to clarify there are fonts installed, they're just not active

Step-by-step reproduction instructions

• Go to the Site editor > Styles > Typography
• Make sur eto have some fonts installed.
• Deactivate all fonts.
• Close the fonts modal dialog
• Observe the 'No fonts installed.' text in the Styles panel
• Observe the 'Add fonts' button text

Screenshots, screen recording, code snippet

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Environment info

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Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes