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/ResourceProviderHostLoader.cs

@@ -0,0 +1,82 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Microsoft.SqlTools.Extensibility;
+using Microsoft.SqlTools.Hosting;
+using Microsoft.SqlTools.Hosting.Protocol;
+using Microsoft.SqlTools.ServiceLayer.SqlContext;
+using Microsoft.SqlTools.Utility;
+
+namespace  Microsoft.SqlTools.ResourceProvider
+{
+    /// <summary>
+    /// Provides support for starting up a service host. This is a common responsibility
+    /// for both the main service program and test driver that interacts with it
+    /// </summary>
+    public static class ResourceProviderHostLoader
+    {
+        private static object lockObject = new object();
+        private static bool isLoaded;
+
+        internal static UtilityServiceHost CreateAndStartServiceHost(SqlToolsContext sqlToolsContext)
+        {
+            UtilityServiceHost serviceHost = UtilityServiceHost.Instance;
+            lock (lockObject)
+            {
+                if (!isLoaded)
+                {
+                    // Grab the instance of the service host
+                    serviceHost.Initialize();
+
+                    InitializeRequestHandlersAndServices(serviceHost, sqlToolsContext);
+
+                    // Start the service only after all request handlers are setup. This is vital
+                    // as otherwise the Initialize event can be lost - it's processed and discarded before the handler
+                    // is hooked up to receive the message
+                    serviceHost.Start().Wait();
+                    isLoaded = true;
+                }
+            }
+            return serviceHost;
+        }
+
+        private static void InitializeRequestHandlersAndServices(UtilityServiceHost serviceHost, SqlToolsContext sqlToolsContext)
+        {
+            // Load extension provider, which currently finds all exports in current DLL. Can be changed to find based
+            // on directory or assembly list quite easily in the future
+            ExtensionServiceProvider serviceProvider = ExtensionServiceProvider.CreateDefaultServiceProvider();
+            serviceProvider.RegisterSingleService(sqlToolsContext);
+            serviceProvider.RegisterSingleService(serviceHost);
+
+            // CredentialService.Instance.InitializeService(serviceHost);
+            // serviceProvider.RegisterSingleService(CredentialService.Instance);
+
+            InitializeHostedServices(serviceProvider, serviceHost);
+
+            serviceHost.InitializeRequestHandlers();
+        }
+
+        /// <summary>
+        /// Internal to support testing. Initializes <see cref="IHostedService"/> instances in the service,
+        /// and registers them for their preferred service type
+        /// </summary>
+        internal static void InitializeHostedServices(RegisteredServiceProvider provider, IProtocolEndpoint host)
+        {
+            // Pre-register all services before initializing. This ensures that if one service wishes to reference
+            // another one during initialization, it will be able to safely do so
+            foreach (IHostedService service in provider.GetServices<IHostedService>())
+            {
+                provider.RegisterSingleService(service.ServiceType, service);
+            }
+
+            foreach (IHostedService service in provider.GetServices<IHostedService>())
+            {
+                // Initialize all hosted services, and register them in the service provider for their requested
+                // service type. This ensures that when searching for the ConnectionService you can get it without
+                // searching for an IHostedService of type ConnectionService
+                service.InitializeService(host);
+            }
+        }
+    }
+}