Hygiene: collapse mobile.search LESS into mobile.startup

MinervaNeue depends on mobile.search. mobile.search's LESS has been
collapsed into mobile.startup. This patch updates Minerva's references
and revises the SearchOverlay's CSS selector to increase specificity to
account for the new order of CSS files. Previously:

- ...
- MobileFrontend Overlay.less
- MobileFrontend SearchOverlay.less
- ...
- Minerva Overlay.less
- Minerva SearchOverlay.less
- ...

Now:

- ...
- MobileFrontend Overlay.less
- Minerva Overlay.less
- ...
- MobileFrontend SearchOverlay.less
- Minerva SearchOverlay.less
- ...

Since SearchOverlay's selector are intended to override Overlay's, it
seems appropriate to specify that a SearchOverlay is also an Overlay and
increase specificity.

Bug: T210207
Related: Ib0316020ed10eb0c921a3300501df7634a889977
Change-Id: I5c06b13f22f530fb52f37f373e081ed55f332a07

skin.json

@@ -125,7 +125,8 @@
 				"skinStyles/mobile.startup/skin.less",
 				"skinStyles/mobile.startup/toast.less",
 				"skinStyles/mobile.startup/Overlay.less",
-				"skinStyles/mobile.startup/toggle.less"
+				"skinStyles/mobile.startup/toggle.less",
+				"skinStyles/mobile.startup/search/SearchOverlay.less"
 			],
 			"mediawiki.special": [
 				"skinStyles/mobile.special.styles/minerva.less"
@@ -142,9 +143,6 @@
 			"mediawiki.action.edit.styles": [
 				"skinStyles/mediawiki.action.edit.styles/minerva.less"
 			],
-			"mobile.search": [
-				"skinStyles/mobile.search/SearchOverlay.less"
-			],
 			"mobile.special.mobilemenu.styles": [
 				"skinStyles/mobile.special.mobilemenu.styles/minerva.less"
 			],

skinStyles/mobile.startup/search/SearchOverlay.less

@@ -1,10 +1,10 @@
-@import '../../minerva.less/minerva.variables';
+@import '../../../minerva.less/minerva.variables';
 
 // These styles transform the SearchOverlay appearance in the Minerva skin.
 // Since SearchOverlay can be used by other skins, these styles are kept separate from
 // the others.
 
-.search-overlay {
+.overlay.search-overlay {
 	.spinner-container {
 		top: @headerHeight;
 	}
@@ -18,7 +18,7 @@
 }
 
 @media all and ( min-width: @width-breakpoint-tablet ) {
-	.search-overlay {
+	.overlay.search-overlay {
 		.search-box {
 			display: table-cell;
 		}
@@ -47,7 +47,7 @@
 }
 
 @media all and ( min-width: @width-breakpoint-desktop ) {
-	.search-overlay {
+	.overlay.search-overlay {
 		.overlay-content {
 			// align with the search form
 			max-width: @contentMaxWidthTablet + ( 2 * @iconGutterWidth );