hygiene: Make LESS imports non-ambigious

Some LESS parsers will get confused with the lack of file extension.
It's better to be explicit and in alignment with recent change in core
I379334d7729e587a2a00.
It was already weirdly mixed in this repo with some imports featuring
extension and some not.

Change-Id: If5065cf9e30289de9b4fd33315bd65b75959ecb7

components/common.less

@@ -3,7 +3,7 @@
  * prepended with @noflip in a comment block.
  *
  */
-@import 'mediawiki.mixins';
+@import 'mediawiki.mixins.less';
 
 /* Framework */
 html {

components/navigation.less

@@ -1,7 +1,7 @@
-@import 'mediawiki.mixins';
-@import 'personalNavigation';
-@import 'search';
-@import 'tabs';
+@import 'mediawiki.mixins.less';
+@import 'personalNavigation.less';
+@import 'search.less';
+@import 'tabs.less';
 
 /* Hide, but keep accessible for screen-readers */
 #mw-navigation h2 {

components/search.less

@@ -1,5 +1,5 @@
-@import 'mediawiki.mixins';
-@import 'mediawiki.ui/variables';
+@import 'mediawiki.mixins.less';
+@import 'mediawiki.ui/variables.less';
 
 /* Search */
 #p-search {

components/tabs.less

@@ -1,5 +1,5 @@
-@import '../variables';
-@import 'mediawiki.mixins';
+@import '../variables.less';
+@import 'mediawiki.mixins.less';
 
 /**
  * Styling for namespace tabs (page, discussion) and views (read, edit, view history, watch and other actions)

components/watchstar.less

@@ -1,5 +1,5 @@
-@import '../variables';
-@import 'mediawiki.mixins.rotation';
+@import '../variables.less';
+@import 'mediawiki.mixins.rotation.less';
 
 /* Watch/Unwatch Icon Styling */
 /* Only use icon if the menu item is not collapsed into the "More" dropdown

responsive.less

@@ -3,7 +3,7 @@
 	instead of to the side of it. They also hide the logo, as there's no space
 	left for it.
 */
-@import 'mediawiki.ui/variables';
+@import 'mediawiki.ui/variables.less';
 
 @media screen and ( max-width: @width-breakpoint-tablet ) {
 	#mw-head {

skinStyles/mediawiki.notification.less

@@ -1,4 +1,4 @@
-@import 'mediawiki.ui/variables';
+@import 'mediawiki.ui/variables.less';
 @import '../variables.less';
 
 /* mediawiki.notification */

variables.less

@@ -1,4 +1,4 @@
-@import 'mediawiki.ui/variables';
+@import 'mediawiki.ui/variables.less';
 
 @font-size-root: 100%;
 @font-size-browser: 16; // Assumed browser default of `16px`