Create feature flag for VectorTitleAboveTabs feature

Adds a feature called VectorTitleAboveTabs that will be used to
toggle a forthcoming feature that moves the page title above the
tabs (the ones that link to talk/history etc).

Bug: T303549
Change-Id: Ibadb4293eca16a83e5e7a9f90ddcf51fab0a0e41

includes/Constants.php

@@ -264,6 +264,26 @@ final class Constants {
 	 */
 	public const WEB_AB_TEST_ARTICLE_ID_FACTORY_SERVICE = 'WikimediaEvents.WebABTestArticleIdFactory';
 
+	/**
+	 * @var string
+	 */
+	public const REQUIREMENT_TITLE_ABOVE_TABS = 'TitleAboveTabs';
+
+	/**
+	 * @var string
+	 */
+	public const CONFIG_TITLE_ABOVE_TABS = 'VectorTitleAboveTabs';
+
+	/**
+	 * @var string
+	 */
+	public const QUERY_PARAM_TITLE_ABOVE_TABS = 'titleabovetabs';
+
+	/**
+	 * @var string
+	 */
+	public const FEATURE_TITLE_ABOVE_TABS = 'TitleAboveTabs';
+
 	/**
 	 * This class is for namespacing constants only. Forbid construction.
 	 * @throws FatalError

includes/ServiceWiring.php

@@ -217,6 +217,29 @@ return [
 			]
 		);
 
+		// Feature: Title above tabs
+		// ================================
+		$featureManager->registerRequirement(
+			new OverridableConfigRequirement(
+				$services->getMainConfig(),
+				$context->getUser(),
+				$context->getRequest(),
+				null,
+				Constants::CONFIG_TITLE_ABOVE_TABS,
+				Constants::REQUIREMENT_TITLE_ABOVE_TABS,
+				Constants::QUERY_PARAM_TITLE_ABOVE_TABS,
+				null
+			)
+		);
+
+		$featureManager->registerFeature(
+			Constants::FEATURE_TITLE_ABOVE_TABS,
+			[
+				Constants::REQUIREMENT_FULLY_INITIALISED,
+				Constants::REQUIREMENT_TITLE_ABOVE_TABS,
+			]
+		);
+
 		return $featureManager;
 	}
 ];

includes/SkinVector22.php

@@ -167,6 +167,7 @@ class SkinVector22 extends SkinVector {
 					Constants::FEATURE_STICKY_HEADER_EDIT
 				)
 			) : false,
+			'is-title-above-tabs' => $featureManager->isFeatureEnabled( Constants::FEATURE_TITLE_ABOVE_TABS )
 		];
 	}
 }

skin.json

@@ -511,6 +511,10 @@
 		"VectorTableOfContentsCollapseAtCount": {
 			"value": 20,
 			"description": "@var When `VectorTableOfContents` is enabled, the minimum number of headings required to collapse all headings in the sticky table of contents by default."
+		},
+		"VectorTitleAboveTabs": {
+			"value": false,
+			"description": "@var boolean `VectorTitleAboveTabs` places the tittle of the page above the tabs that link to history/talk etc."
 		}
 	},
 	"ServiceWiringFiles": [