Block Bindings: UI components that show connected values should be readonly and not disabled

[afercia]

Description

I followed instructions from WordPress/wordpress-develop#5888 to test the connected blocks in the editor UI. I see that, so far, components in the editor UI that show the connected values are disabled by the means of a disabled HTML attribute.

For example, when an image alt attribute is connected to a post meta source, the alternative text textarea in the Settings panel is disabled:

There's a few problem with this:

• The whole concept of connected attributes is that their content comes from another source. As such, they cannot be edited. Semantically, they are read-only attributes and the UI should communicate that.
• Disabled controls cannot be focused. As such, their value can't be selected and copied.
• Since disabled controls aren't required to have a sufficient color contrawt ration, they're styled in a way that their content is eay less readable. However, users may still want to read their value.
• Screen readers may ignore the associated descriptive text Connected to a custom field as it doesn't make sense to provide a description for a control that is disabled in the first place. In my testing, Safari + VoiceOver don't make the description available to users.

Rather, the control should be readonly.

• The readonly attribute better communicates the attribute cannot be edited but it's still functional.
• The value can be selected and copied.
• The applied styling makes the value way more readable (see screenshot below).
• Screen readers do provide the associated description of readonly controls.

Screenshot with readonly instead of disabled:

In my testing I've gone only through the image alt attribute so far but this applies to any other control of the editor that shows connected values.

Step-by-step reproduction instructions

• Follow instructions from Add the Block Bindings API wordpress-develop#5888 to make an image block alt text connected to a post meta.
• Select the Image block.
• Observe the Alternative Text control (a textarea element) in the Settings sidebar is disabled.

Screenshots, screen recording, code snippet

No response

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