Use ARIA button class on plugin and theme auto-updates action links

[audrasjb]

This ticket is a follow-up to #50512 which raises 4 independent issues related to plugin and theme auto-updates feature.

Props should go to @ryokuhi who summarized the issue.

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Currently, Enable / Disable controls are links. According to the ​accessibility coding standards (see the third row in the table):

• the control should be a link when JavaScript is not available and a button the rest of the time.

According to the current implementation, instead:

• when JavaScript is off, the links work because they have a working href attribute;
• when JavaScript is on, the links behave like buttons, but they’re still perceived as links.

A partial solution would be to add the CSS class aria-button-if-js, that adds a role=button for these cases; this doesn't make the link-as-button work through spacebar as expected, though.

[audrasjb]

Partially fixes the issue by adding aria-button-if-js class to action links

[afercia]

50516.2.diff​ makes all the auto-updates toggle controls be perceived and behave like buttons. Also:

1. wp_theme_auto_update_setting_template() is only used for the tmpl-theme-single JS template. This means that with JS off, this template won't be rendered. All the links with a href attribute for no-JS support used here are a bit pointless. These can be button elements.
2. Adds keyup and keydown events to make these controls behave like buttons: activated when the Spacebar is released and preventing the page from scrolling when the Spacebar is pressed.
3. Avoids to update the href attribute when the controls are buttons (which don't have a href).
4. Avods to target elements based on their type: since the markup may change at any time, it's better to not use element selectors.
5. Changes a speak message from "Enable auto-updates" to "Auto-updates enabled".
6. Removes the polite argument from the wp.a11y.speak() calls, as polite is the default value .
7. Minor CSS improvements.
8. Minor JS coding standards.

Some testing would be nice :)

[whyisjake]

Love the spacebar controls.

[whyisjake]

In 48418:

Upgrade/Install: Use ARIA button class on plugin and theme auto-updates action links

According to the [accesability guidelines](​https://developer.wordpress.org/coding-standards/wordpress-coding-standards/accessibility/#semantics-for-controls), the control should be a link when JavaScript is not available and a button the rest of the time.

In addition, handlers were added for spacebar usage, and some changes to the a11y speak verbiage.

Fixes #50516.
Props ryokuhi, audrasjb, afercia, whyisjake/

[SergeyBiryukov]

In 48428:

Themes: Correct closing tag for the "Enable auto-updates" button in the JS template for theme auto-update setting.

Follow-up to [48418].

See #50516.