HTML API: Join successive text nodes in html5lib test representation.

Many tests from the html5lib test suite fail because of differences in
text handling between a DOM API and the HTML API, even though the
semantics of the parse are equivalent. For example, it's possible in
the HTML API to read multiple successive text nodes when the tokens
between them are ignored.

The test suite didn't account for this and so was failing tests. This
patch improves the construction of the representation to compare
against the test suite so that those tests don't fail inaccurately.

Developed in https://github.com/WordPress/wordpress-develop/pull/6984
Discussed in https://core.trac.wordpress.org/ticket/61576

Props bernhard-reiter, dmsnell, jonsurrell.
See #61576.

Built from https://develop.svn.wordpress.org/trunk@58712


git-svn-id: http://core.svn.wordpress.org/trunk@58114 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-alpha-58710';
+$wp_version = '6.7-alpha-58712';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.