[WIP] Fix UNC path on Windows

Fixes #1152

Signed-off-by: David Thompson <davthomp@redhat.com>

Author: datho7561

org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/uriresolver/CacheResourceFileNotFoundException.java

@@ -0,0 +1,9 @@
+package org.eclipse.lemminx.uriresolver;
+
+public class CacheResourceFileNotFoundException extends CacheResourceException {
+
+	public CacheResourceFileNotFoundException(String resourceURI, String message) {
+		super(resourceURI, message);
+	}
+	
+}

org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/uriresolver/CacheResourcesManager.java

@@ -14,6 +14,7 @@
 
 import static org.eclipse.lemminx.utils.ExceptionUtils.getRootCause;
 
+import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -26,6 +27,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.text.MessageFormat;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -165,6 +167,16 @@ public Path getResource(final String resourceURI) throws IOException {
 					CacheResourceDownloadingError.DOWNLOAD_DISABLED, null, null);
 		}
 
+		URI resourceUriParsed = URI.create(resourceURI);
+		if ("file".equals(resourceUriParsed.getScheme())) {
+			// UNC path
+			Path path = Path.of(resourceUriParsed);
+			if (!Files.exists(path)) {
+				throw new CacheResourceFileNotFoundException(path.toString(), "The network-accessible file '" + path.toString() + "' doesn't exist");
+			}
+			return path;
+		}
+
 		if (!FilesUtils.isIncludedInDeployedPath(resourceCachePath)) {
 			throw new CacheResourceDownloadingException(resourceURI, resourceCachePath,
 					CacheResourceDownloadingError.RESOURCE_NOT_IN_DEPLOYED_PATH, null, null);
@@ -309,6 +321,7 @@ public static Path getResourceCachePath(String resourceURI) throws IOException {
 	}
 
 	public static Path getResourceCachePath(URI uri) throws IOException {
+
 		// Eliminate all path traversals
 		URI normalizedUri = uri.normalize();