The Shadow Range controls are unlabeled

[afercia]

Description

Discovered while testing #63874

All the range controls in the Shadows popover are unlabeled. Screenshot:

Step-by-step reproduction instructions

• Go to the Site editor > Styles > Shadows
• Edit one of the shadows.
• Inspect the source and observe all the 4 sliders are unlabeled: X Position, Y Position, Blur, Spread.

Screenshots, screen recording, code snippet

No response

Environment info

No response

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

[afercia]

Introduced in #60706

Additionally:

• The visible text: X Position, Y Position, Blur, Spread., are H2 headings. It would be best to use real, visible, label elements.
• Teh popover title is a H5 heading, which doesn't make sense in the headings hierarchy.

[afercia]

Noting that the design is inconsistent, as the toggle to switch the control to the input to enter a custom value is always placed after the control in the editor. Instead, in this case it's placed after the title of the control, which is less than ideal.

Example of other controls:

The best way to solve this issue is by changing the design, which would also make it consistent with other controls.

[afercia]

As far as I can tell, this is the only Popover that has a visible title. It's a H5 heading, which is an arbitrary level in the headings hierarchy. Most popovers don't have a visible title, e.g. the Color picker in the screenshot below. Sometimes they do have an aria-label but don't have an ARIA role so that's incorrect anyways.
To fix the design and semantics inconsistency my preference would be to render a visible title for all popovers and reference it with aria-labelledby to label the popover. Lastly, the popover should be a non-modal dialog. I'll split this into a separate issue.