Move "Return to comment" below sticky header when present

Also ensure that when we click the button, we scroll the widget fully
into view below the sticky header.

Bug: T318474
Change-Id: I394f02912cd6ab2773552a7364691ef89a17369c

.stylelintrc.json

@@ -4,7 +4,7 @@
 		"stylelint-config-wikimedia/mediawiki"
 	],
 	"rules": {
-		"selector-class-pattern": "^(ext|ve|mw|oo-ui|client|skin|mf)-",
+		"selector-class-pattern": "^(ext|ve|mw|oo-ui|client|skin|mf|vector)-",
 		"unit-disallowed-list": null
 	}
 }

modules/CommentController.js

@@ -4,7 +4,11 @@ var
 	logger = require( './logger.js' ),
 	dtConf = require( './config.json' ),
 	CommentItem = require( './CommentItem.js' ),
-	scrollPadding = { top: 10, bottom: 10 },
+	scrollPadding = {
+		// eslint-disable-next-line no-jquery/no-class-state
+		top: 10 + ( $( document.body ).hasClass( 'vector-feature-sticky-header-enabled' ) ? 50 : 0 ),
+		bottom: 10
+	},
 	defaultEditMode = mw.user.options.get( 'discussiontools-editmode' ) || mw.config.get( 'wgDiscussionToolsFallbackEditMode' ),
 	defaultVisual = defaultEditMode === 'visual',
 	featuresEnabled = mw.config.get( 'wgDiscussionToolsFeaturesEnabled' ) || {},

modules/dt.ui.ReplyWidget.less

@@ -52,6 +52,10 @@
 		transform: translate( -50%, -150% );
 		top: 0;
 		left: 50%;
+
+		.vector-sticky-header-visible & {
+			top: 50px;
+		}
 	}
 
 	&-scrollback-bottom {
@@ -60,6 +64,7 @@
 		left: 50%;
 	}
 
+	// stylelint-disable-next-line no-descending-specificity
 	&-scrollback-top,
 	&-scrollback-bottom {
 		position: fixed;