Use two new sniffs from PHPCSExtra 1.2.0

PHPCSExtra 1.2.0 was released yesterday and contains two new sniffs which IMO would be suitable for adding to WordPressCS.

Includes raising the minimum supported PHPCSExtra version. (will conflict with PR 2408 and will need rebase depending on which is merged first)

Ref:
* https://github.com/PHPCSStandards/PHPCSExtra/releases/tag/1.2.0

Author: jrfnl

.github/CONTRIBUTING.md

@@ -41,7 +41,7 @@ When you introduce new `public` sniff properties, or your sniff extends a class
 * WordPress-Coding-Standards
 * PHP_CodeSniffer 3.7.2 or higher
 * PHPCSUtils 1.0.8 or higher
-* PHPCSExtra 1.1.0 or higher
+* PHPCSExtra 1.2.0 or higher
 * PHPUnit 4.x, 5.x, 6.x or 7.x
 
 The WordPress Coding Standards use the `PHP_CodeSniffer` native unit test framework for unit testing the sniffs.

WordPress-Core/ruleset.xml

@@ -869,6 +869,9 @@
 	<!-- Important to prevent issues with content being sent before headers. -->
 	<rule ref="Generic.Files.ByteOrderMark"/>
 
+	<!-- Always have a lowertag PHP open tag. -->
+	<rule ref="Universal.PHP.LowercasePHPTag"/>
+
 	<!-- All line endings should be \n. -->
 	<rule ref="Generic.Files.LineEndings">
 		<properties>

WordPress-Extra/ruleset.xml

@@ -180,6 +180,9 @@
 	<!-- Detect useless "echo sprintf(...)". -->
 	<rule ref="Universal.CodeAnalysis.NoEchoSprintf"/>
 
+	<!-- Detect use of double negative `!!`. -->
+	<rule ref="Universal.CodeAnalysis.NoDoubleNegative"/>
+
 	<!--
 	#############################################################################
 	Code style sniffs for more recent PHP features and syntaxes.

composer.json

@@ -23,7 +23,7 @@
 		"ext-xmlreader": "*",
 		"squizlabs/php_codesniffer": "^3.7.2",
 		"phpcsstandards/phpcsutils": "^1.0.8",
-		"phpcsstandards/phpcsextra": "^1.1.0"
+		"phpcsstandards/phpcsextra": "^1.2.0"
 	},
 	"require-dev": {
 		"phpcompatibility/php-compatibility": "^9.0",