Deprecate e_parse::toJS()

`e_parse::toJS()`, documented with the description

> Convert text blocks which are to be embedded within JS

, does not protect strings from injections, which appears to be its
primary use.  Additionally, it performs multiple unrelated string
modifications:

* Replace Windows line breaks with a literal `\\n` (which would later be
  parsed as `\n` in JavaScript/JSON)
* Does not modify Unix line breaks (`\n`), which is inconsistent with
  the Windows line break behavior
* Removes HTML tags
* Replaces HTML entities as `htmlentities()` does

This method cannot be fixed because its usages are inconsistent.  Most
notably, some usages surround the method's output in single quotes while
others surround it with double quotes.  Strings cannot be JSON-encoded
without confounding quotation mark styles.

All core usages of `e_parse::toJS()` have been replaced with
alternatives, which are also documented in the method's DocBlock.

Fixes: #4546

e107_handlers/e_parse_class.php

@@ -1871,9 +1871,16 @@ class e_parse
 	 *
 	 * @param string|array $stringarray
 	 * @return string
+	 * @deprecated v2.3.1 This method will not escape a string properly for use as a JavaScript or JSON string. Use
+	 *             {@see e_parse::toJSON()} instead. When using {@see e_parse::toJSON()}, do not surround its output
+	 *             with quotation marks, and do not attempt to escape sequences like "\n" as "\\n". If HTML tags need to
+	 *             be removed, consider {@see e_parse::toText()} separately. If the text needs to be used in an HTML
+	 *             tag attribute (e.g. <a onclick="ATTRIBUTE"></a>), surround the string with
+	 *             {@see e_parse::toAttribute()} and either single-quote or double-quote the attribute value.
 	 */
 	public function toJS($stringarray)
 	{
+		trigger_error('<b>' . __METHOD__ . ' is deprecated. See method DocBlock for alternatives.</b>', E_USER_WARNING); // NO LAN
 
 		$search = array("\r\n", "\r", '<br />', "'");
 		$replace = array("\\n", '', "\\n", "\'");