Support HDFS Tiering (#7484)

This is the 1st step to supporting HDFS Tiering
Changes:

Add new mounted folder icon. Will have separate commit for file icon
Disable delete/mkdir/upload for mounted files and folders
Disable delete for root HDFS folder (this was added in error)

extensions/mssql/src/hdfs/mount.ts

@@ -0,0 +1,19 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+/**
+ * Information about a HDFS mount to a remote directory
+ */
+export interface Mount {
+	mountPath: string;
+	mountStatus: string;
+	remotePath: string;
+}
+
+export enum MountStatus {
+	None = 0,
+	Mount = 1,
+	Mount_Child = 2
+}