Port Azure code from SSDT to the tools service (#477)

Porting of the vast majority of Azure-related code from SSDT. This is very large, so I want to put this out as one large "lift and shift" PR before I do the tools-service specific JSON-RPC service handlers, connect a new account handler (as the code to get necessary info from accounts and subscriptions isn't fully complete) and add tests over these

**What's in this PR**:

- Created 3 new projects:
  - Microsoft.SqlTools.ResourceProvider will host the executable that accepts requests for Azure-related actions over the JSON-RPC protocol. This must be separate from other DLLs since a direct dependency on the Azure SDK DLLs fails (they're NetStandard 1.4 and you can't reference them if you have RuntimeIdentifiers in your .csproj file)
  - Microsoft.SqlTools.ResourceProvider.Core is where all the main business logic is, including definitions and logic on how to navigate over resources and create firewall rules, etc.
  - Microsoft.SqlTools.ResourceProvider.DefaultImpl is the actual Azure implementation of the resource provider APIs. The reason for separating this is to support eventual integration back into other tools (since their Azure and Identity services will be different).
- Implemented the AzureResourceManager that connects to Azure via ARM APIs and handles creating firewall rule and querying databases. The dependent DLLs have had major breaking changes, so will need additional verification to ensure this works as expected
- Ported the unit tests for all code that was not a viewmodel. Viewmodel test code will be ported in a future update as we plumb through a service-equivalent to these. Also, the DependencyManager code which has overlap with our service provider code is commented out. Will work to uncomment in a future update as it has value to test some scenarios

**What's not in this PR**:
- Identity Services. We currently just have a stub for the interface, and even that will likely change a little
- anything JSON-RPC or registered service related. These will be adapted from the viewmodels and added in a separate PR

src/Microsoft.SqlTools.ResourceProvider/Program.cs

@@ -0,0 +1,63 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.IO;
+using Microsoft.SqlTools.Hosting.Utility;
+using Microsoft.SqlTools.ServiceLayer.SqlContext;
+using Microsoft.SqlTools.Utility;
+
+namespace Microsoft.SqlTools.ResourceProvider
+{
+    /// <summary>
+    /// Main application class for Credentials Service Host executable
+    /// </summary>
+    internal class Program
+    {
+        private const string ServiceName = "SqlToolsAzure.exe";
+
+        /// <summary>
+        /// Main entry point into the Credentials Service Host
+        /// </summary>
+        internal static void Main(string[] args)
+        {
+            try
+            {
+                // read command-line arguments
+                CommandOptions commandOptions = new CommandOptions(args, ServiceName);
+                if (commandOptions.ShouldExit)
+                {
+                    return;
+                }
+
+                string logFilePath = "sqltoolsazure";
+                if (!string.IsNullOrWhiteSpace(commandOptions.LoggingDirectory))
+                {
+                    logFilePath = Path.Combine(commandOptions.LoggingDirectory, logFilePath);
+                }
+
+                // turn on Verbose logging during early development
+                // we need to switch to Normal when preparing for public preview
+                Logger.Initialize(logFilePath: logFilePath, minimumLogLevel: LogLevel.Verbose, isEnabled: commandOptions.EnableLogging);
+                Logger.Write(LogLevel.Normal, "Starting SqlTools Azure Provider");
+
+                // set up the host details and profile paths 
+                var hostDetails = new HostDetails(
+                    name: "SqlTools Azure Provider",
+                    profileId: "Microsoft.SqlTools.ResourceProvider",
+                    version: new Version(1, 0));
+
+                SqlToolsContext sqlToolsContext = new SqlToolsContext(hostDetails);
+                UtilityServiceHost serviceHost = ResourceProviderHostLoader.CreateAndStartServiceHost(sqlToolsContext);
+
+                serviceHost.WaitForExit();
+            }
+            catch (Exception e)
+            {
+                Logger.Write(LogLevel.Error, string.Format("An unhandled exception occurred: {0}", e));
+                Environment.Exit(1);               
+            }
+        }
+    }
+}