Scripts: Remove special behaviors for non-HTML5 scripts

[sirreal]

Trac ticket: https://core.trac.wordpress.org/ticket/64442

HTML5 script theme support is not worth considering today, themes do not control and are not concerned with HTML5 script rendering. Data suggests that the overwhelming majority of page views are HTML5, not XHTML (props @westonruter) and theme scripts are not broken regardless of their declared support.

This declared support has two impacts, it will add a type attribute to script tags and it will add CDATA wrappers.

This is an inline script without declared HTML5 script support:

<script type="text/javascript" async="async">
/* <![CDATA[ */
"script contents";
/* ]]> */
</script>

And the same script with support:

<script async>
"script contents";
</script>

#64428 proposes removal of the type attribute on scripts and styles. This ticket focuses on all aspects of theme support for HTML5 scripts. Declaring HTML5 script support can be deprecated, and the CDATA and type attribute removed.

The CDATA wrappers are redundant for JavaScript in HTML5 and are harmful where script tags do not contain JavaScript (#60320). The HTML5 checks add needless complication to code.

The redundant attribute and CDATA wrappers are only relevant for XHTML. This requires the appropriate Content-Type: application/xhtml+xml HTTP header to be sent, something that themes do not appear to do. The HTTP content type header is more closely tied to server configuration (PHP defaults to text/html) than theme support. Themes do not really know whether a page will be served and interpreted as XHTML.

This is part of #59883.
Related to #64428 and #64419.

Related to #10658.

To do:

• Remove the ::add_html5_script_theme_support() method from script tests. Depends on ticket 64428 (Scripts and styles: Remove redundant HTML5 type attributes #10658)
  

  wordpress-develop/tests/phpunit/tests/dependencies/scripts.php

  Lines 3612 to 3617 in 3d9fde3

  	/**
  	* Adds html5 script theme support.
  	*/
  	protected function add_html5_script_theme_support() {
  	add_theme_support( 'html5', array( 'script' ) );
  	}

• Review html5 behavior in tests/phpunit/tests/dependencies/wpInlineScriptTag.php (type attribute and CDATA behaviors).

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[github-actions]

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[github-actions]

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Props jonsurrell.

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[westonruter]

So great to remove this tech debt!