Make lazy collectiing of Workspace Artifacts in completion

Make Maven Projects to be loaded/cached lazily when collecting the Workspace Artifacts
when gathering completions n order to make content assist faster and more responsive

Issue: eclipse-lemminx#444

lemminx-maven/src/main/java/org/eclipse/lemminx/extensions/maven/MavenLemminxExtension.java

@@ -224,14 +224,17 @@ private synchronized CompletableFuture<Void> getOrCreateMavenInitializer() {
 		// while Maven component is initializing.
 		if (mavenInitializer == null) {
 			if (isUnitTestMode()) {
+				mavenInitializer = new CompletableFuture<>();
 				doInitialize(() -> {});
-				mavenInitializer = CompletableFuture.completedFuture(null);
+				mavenInitializer.complete(null);
 			} else
 				mavenInitializer = CompletableFutures.computeAsync(cancelChecker -> {
 					doInitialize(cancelChecker);
 					return null;
 				});
 		}
+		// Start Maven Project Cache
+		mavenInitializer.thenAccept(t -> cache.initialized());
 		return mavenInitializer;
 	}
 
@@ -693,12 +696,28 @@ public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IO
 	/**
 	 * Returns the list of Maven Projects currently added to the Workspace
 	 * 
+	 * @param buildIfNecessary A boolean 'true' indicates that all projects are to
+	 *                         be returned, not only the cached ones at the moment,
+	 *                         method should wait for the final build result,
+	 *                         otherwise the only project that are already built and
+	 *                         cached are to be returned, the rest of the projects
+	 *                         are to be built in background
 	 * @return List of Maven Projects
 	 */
-	public List<MavenProject> getCurrentWorkspaceProjects() {
-		return workspaceReader.getCurrentWorkspaceArtifactFiles().stream()
-			.map(f -> getProjectCache().getLastSuccessfulMavenProject(f))
-			.filter(Objects::nonNull).toList();
+	public List<MavenProject> getCurrentWorkspaceProjects(boolean wait) {
+		if (wait) {
+			return workspaceReader.getCurrentWorkspaceArtifactFiles().stream()
+					.map(file -> getProjectCache().getLastSuccessfulMavenProject(file))
+					.filter(Objects::nonNull)
+					.toList();
+		} else {
+			return workspaceReader.getCurrentWorkspaceArtifactFiles().stream()
+				.map(file -> getProjectCache().assyncGetLoadedMavenProject(file))
+				.map(f -> f.getNow(null))
+				.filter(Objects::nonNull)
+				.map(LoadedMavenProject::getMavenProject)
+				.toList();
+		}
 	}
 
 	/**