[Library | new-theme]: Create common methods to get entity name and entity file name from OpenaireEntities.

1. string-utils.class.ts:
   a. Added method "public static getEntityName(entityType: string, plural: boolean = false): string" to return OpenaireEntities name by entityType.
   b. Added method "public static getEntityFileName(entityType: string): string" to return OpenaireEntities file name by entityType.
2. directLinking.component.ts & dataProvider.component.ts & project.component.ts & resultLanding.component.ts & myOrcidLinks.component.ts & searchResearchResults.component.ts & result-preview.component.ts & search-tab.component.ts: Call StringUtils.getEntityName and StringUtils.getEntityFileName methods instead of checking if/then/else locally.

explore/src/app/openaireLibrary

@@ -1 +1 @@
-Subproject commit c69ff39d03a2d90f4702f2807c9a861d791ec268
+Subproject commit b88c65a3430a3689770e40e1e6f34d8bb10b86c3