Fix style conflict with content using class="header"

Content using `header` as a CSS class was affected by skin styles
in Minerva being insufficiently specific to the skin‑specific elements.

This changes Minerva to use `class="minerva‑header"`, thus avoiding
the conflict and matching what Vector does.

Bug: T172626
Change-Id: Id8fbe61b2d1d4a89ec11ddfdf7837be797b3bd20

includes/Skins/skin.mustache

@@ -2,7 +2,7 @@
 	<div id="mw-mf-page-center">
 		<a class="mw-mf-page-center__mask" href="#"></a>
 		<header class="header-container header-chrome">
-			<form class="header" action="{{wgScript}}" method="get">
+			<form class="minerva-header" action="{{wgScript}}" method="get">
 				<nav class="navigation-drawer toggle-list view-border-box">
 					<input type="checkbox" id="main-menu-input" class="toggle-list__checkbox" role="button" aria-labelledby="mw-mf-main-menu-button">
 					<label for="main-menu-input" id="mw-mf-main-menu-button"

resources/skins.minerva.base.styles/content/tablet/common.less

@@ -10,7 +10,8 @@ A file for css that optimises the Minerva skin on larger devices.
 		display: none;
 	}
 
-	.header {
+	.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+	.minerva-header {
 		.branding-box {
 			width: @brandingBoxWidth;
 		}
@@ -90,8 +91,8 @@ A file for css that optimises the Minerva skin on larger devices.
 @media screen and ( min-width: @width-breakpoint-desktop ) {
 	// stylelint-disable-next-line selector-max-id
 	.banner-container,
-	/* FIXME: Generic header class needed me-thinks! */
-	.header,
+	.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+	.minerva-header,
 	.page-header-bar,
 	.overlay-header,
 	/* FIXME: Generic content class needed? */
@@ -108,7 +109,8 @@ A file for css that optimises the Minerva skin on larger devices.
 		max-width: @contentMaxWidthTablet;
 	}
 
-	.header {
+	.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+	.minerva-header {
 		// Make sure the main menu and secondary button icon images are aligned
 		// with the content.
 		max-width: @contentMaxWidthTablet + 2 * @iconGutterWidth;

resources/skins.minerva.base.styles/print/header.less

@@ -5,7 +5,8 @@
 	box-shadow: none !important;
 }
 
-.header {
+.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+.minerva-header {
 	border-top: 0;
 	display: block;
 	height: auto;

resources/skins.minerva.base.styles/print/styles.less

@@ -4,7 +4,8 @@
 @media print {
 	.noprint,
 	.banner-container,
-	.header,
+	.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+	.minerva-header,
 	.minerva__tab-container,
 	.page-actions-menu,
 	.post-content {

resources/skins.minerva.base.styles/ui.less

@@ -57,7 +57,8 @@ main {
 	display: none;
 }
 
-.header {
+.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+.minerva-header {
 	display: table;
 	width: 100%;
 	border-spacing: 0;
@@ -120,8 +121,9 @@ main {
 }
 
 .search-box,
-/* `.header .search-box` is needed to override table-cell rules */
-.header .search-box {
+/* `.minerva-header .search-box` is needed to override table-cell rules */
+.header .search-box, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+.minerva-header .search-box {
 	display: none;
 	width: auto;
 }

skinStyles/mediawiki.searchSuggest/index.less

@@ -20,7 +20,8 @@
 	}
 
 	.search-enabled {
-		.header {
+		.header, /* FIXME: Remove once <form class="header"> is no longer in the cache (~1 week) */
+		.minerva-header {
 			position: relative;
 
 			.search-box {