[Library & openaire-theme & Explore | explore-redesign]: Added search form in menu (navbar) in landing pages.

1. search.less: Added css for modifier .small-vertical for .input-wrapper of <search-input>.
2. layout.service.ts: Added hasMenuSearchBarSubject: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(false), parsing and getter/setter methods.
3. navigationBar.module.ts: Imported SearchInputModule.
4. navigationBar.component.ts:
   a. Added searchMode: boolean = false; and hasSearchBar: boolean = false; (and other helpful fields)
   b. Subscribe to queryParams to hide search bar and reset keyword | Subscribe to layoutService.hasMenuSearchBar to check if search should be included in navbar or not.
   c. Added methods "openSearch()" to show the search form and "goTo()" to trigger the search action and navigate to the search page.
5. navigationBar.component.html: Added <div search-input> and search-icon button to show search bar | Added checks if searchMode is enabled (search form visible) or not.
6. app-routing.module.ts: In routes for landing pages added in data: hasMenuSearchBar: true.

less/search.less

@@ -116,6 +116,14 @@
       }
     }
   }
+
+  &.small-vertical {
+    --search-input-icon-padding-vertical: 10px;
+
+    & .search {
+      --input-padding-vertical: 10px;
+    }
+  }
 }
 
 .hook-inverse-misc() {