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#444

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

@@ -33,10 +33,9 @@ public class LoadedMavenProject {
 	private final Collection<ModelProblem> problems;
 	private final DependencyResolutionResult dependencyResolutionResult;
 
-	public LoadedMavenProject(MavenProject mavenProject, int version, Collection<ModelProblem> problems,
+	public LoadedMavenProject(MavenProject mavenProject, Collection<ModelProblem> problems,
 			DependencyResolutionResult dependencyResolutionResult) {
 		this.mavenProject = mavenProject;
-		this.lastCheckedVersion = version;
 		this.problems = problems;
 		this.dependencyResolutionResult = dependencyResolutionResult;
 	}

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

@@ -0,0 +1,124 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Red Hat Inc. and others.
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package org.eclipse.lemminx.extensions.maven;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import org.apache.maven.model.building.FileModelSource;
+import org.eclipse.lemminx.dom.DOMDocument;
+import org.eclipse.lemminx.extensions.maven.utils.DOMModelSource;
+import org.eclipse.lemminx.extensions.maven.MavenProjectCache.ProjectBuildManager;
+
+import org.eclipse.lemminx.services.IXMLDocumentProvider;
+import org.eclipse.lemminx.utils.FilesUtils;
+
+/**
+ * An object aggregating a build results of a Maven Document, controlling the 
+ * asynchronous access to the Maven Project built from the latest version of 
+ * the provided document.
+ */
+public class LoadedMavenProjectProvider {
+	private static final Logger LOGGER = Logger.getLogger(LoadedMavenProjectProvider.class.getName());
+
+	private final String uri;
+	private final IXMLDocumentProvider documentProvider;
+	private final ProjectBuildManager buildManager;
+
+	private int lastCheckedVersion;
+	private CompletableFuture<LoadedMavenProject> future;
+
+	/**
+	 * Creates a LoadedMavenProjectProvider using provided URI String identifying the 
+	 * document to be built into a Maven Project. A document found by using Document 
+	 * Provider is the latest version of the document being currently edited or a document 
+	 * read from a file specified by document URI String.
+	 * 
+	 * @param uri A URI String identifying the document
+	 * @param documentProvider An IXMLDocumentProvider instance used to find the latest 
+	 * 		version of the document
+	 * @param buildManager A MavenProject builder
+	 */
+	public LoadedMavenProjectProvider(String uri, IXMLDocumentProvider documentProvider, ProjectBuildManager buildManager) {
+		this.uri = uri;
+		this.documentProvider = documentProvider;
+		this.buildManager = buildManager;
+		this.lastCheckedVersion = -1;
+	}
+
+	/**
+	 * Returns a `CompletableFuture<LoadedMavenProject>` for asynchronous access
+	 * to the Maven Project built from the latest version of the document.
+	 *  
+	 * @return CompletableFuture of LoadedMavenProject object 
+	 */
+	public CompletableFuture<LoadedMavenProject> getLoadedMavenProject() {
+		DOMDocument document = documentProvider.getDocument(uri);
+		// Check if future must be created
+		// 1. is the future exist?
+		boolean shouldLoad = future == null || future.isCompletedExceptionally();
+		if (!shouldLoad) {
+			// 2. is the current future is not out of dated?
+			if (document != null) {
+				if (lastCheckedVersion !=  document.getTextDocument().getVersion()) {
+					shouldLoad = true;
+				}				
+			}
+		}
+
+		if (shouldLoad) {
+			if (future != null) {
+				future.cancel(true);
+			}
+			if (document != null) {
+				lastCheckedVersion = document.getTextDocument().getVersion();
+			}
+			future = load(uri, document);
+		}
+		return future;
+	}
+
+	private CompletableFuture<LoadedMavenProject> load(String uri, DOMDocument document) {
+		try {
+			FileModelSource source = null;			
+			if (document != null) {
+				source  = new DOMModelSource(document);				
+			} else {
+				source = new FileModelSource(FilesUtils.toFile(uri));
+			}
+			return buildManager.build(uri, source);
+		} catch (Exception e) {
+			LOGGER.log(Level.SEVERE, e.getMessage() + ": " + uri, e);
+			throw e;
+		}
+	}
+
+	/**
+	 * Returns URI String identifying a Maven Project document or file
+	 * 
+	 * @return
+	 */
+	public String getUri() {
+		return uri;
+	}
+
+	/**
+	 * Returns the last checked version of the document of the pom.xml.
+	 * <p>
+	 * 0 means that the loaded maven project has been loaded by a pom.xml file (it
+	 * is not editing).
+	 * </p>
+	 * 
+	 * @return the last checked version of the document of the pom.xml.
+	 */
+	public int getLastCheckedVersion() {
+		return lastCheckedVersion;
+	}
+}