Site Health: show admin notice when JavaScript support is off

[afercia]

As done for all the admin pages that have features that depend on JavaScript support, also the Site Health pages should display an admin notice when JavaScript id disabled.

Also, the pages should probably display no content other than the admin notice. Examples:

Gutenberg:

Theme installer:

Current Site Health status page:

[afercia]

46717.diff​

• displays an error notice when JavaScript is off, consistently with other JavaScript-dependent screens
• keeps the main h1 visible

Minor clean-ups:

• makes code indentation consistent in site-health.php and site-health-info.php
• removes a couple of <div class="wp-clearfix"></div> as that's not the intended usage of wp-clearfix (those divs didn't do anything anyways)

Screenshot:

[afercia]

I guess there's no need for design feedback, as this is pretty standard in core.

[afercia]

46717.2.diff​ updates the notice wording to The Site Health check requires JavaScript.

[afercia]

In 45076:

Administration: Display a notice in the Site Health pages when JavaScript is off.

• displays an error notice when JavaScript is off, consistently with other admin screens that depend on JavaScript
• keeps the main h1 visible

Minor clean-ups:

• makes code indentation consistent in site-health.php and site-health-info.php
• removes a couple of <div class="wp-clearfix"></div> as that's not the intended usage of wp-clearfix (those divs didn't do anything anyways)

Fixes #46717.