Abort when init and run messages fail to process (#2857)

* Abort when init and run messages fail to process, usually on deserialization, to prevent the host from hanging
* Send the message via the abort handler when we abort the run

Author: nohwnd

src/Microsoft.TestPlatform.Common/ExtensionFramework/TestPluginCache.cs

@@ -529,7 +529,7 @@ private Assembly CurrentDomainAssemblyResolve(object sender, AssemblyResolveEven
             {
                 try
                 {
-                    EqtTrace.Verbose("CurrentDomain_AssemblyResolve: Resolving assembly '{0}'.", args.Name);
+                    EqtTrace.Verbose("CurrentDomainAssemblyResolve: Resolving assembly '{0}'.", args.Name);
 
                     if (this.resolvedAssemblies.TryGetValue(args.Name, out assembly))
                     {

src/Microsoft.TestPlatform.Common/Utilities/AssemblyResolver.cs

@@ -106,6 +106,7 @@ private Assembly OnResolve(object sender, AssemblyResolveEventArgs args)
 
             if (this.searchDirectories == null || this.searchDirectories.Count == 0)
             {
+                EqtTrace.Info("AssemblyResolver.OnResolve: {0}: There are no search directories, returning.", args.Name);
                 return null;
             }
 
@@ -146,23 +147,30 @@ private Assembly OnResolve(object sender, AssemblyResolveEventArgs args)
                         continue;
                     }
 
+                    EqtTrace.Info("AssemblyResolver.OnResolve: {0}: Searching in: '{1}'.", args.Name, dir);
+
                     foreach (var extension in SupportedFileExtensions)
                     {
                         var assemblyPath = Path.Combine(dir, requestedName.Name + extension);
                         try
                         {
                             if (!File.Exists(assemblyPath))
                             {
+                                EqtTrace.Info("AssemblyResolver.OnResolve: {0}: Assembly path does not exist: '{1}', returning.", args.Name, assemblyPath);
+
                                 continue;
                             }
 
                             AssemblyName foundName = this.platformAssemblyLoadContext.GetAssemblyNameFromPath(assemblyPath);
 
                             if (!this.RequestedAssemblyNameMatchesFound(requestedName, foundName))
                             {
+                                EqtTrace.Info("AssemblyResolver.OnResolve: {0}: File exists but version/public key is wrong. Try next extension.", args.Name);
                                 continue;   // File exists but version/public key is wrong. Try next extension.
                             }
 
+                            EqtTrace.Info("AssemblyResolver.OnResolve: {0}: Loading assembly '{1}'.", args.Name, assemblyPath);
+                            
                             assembly = this.platformAssemblyLoadContext.LoadAssemblyFromPath(assemblyPath);
                             this.resolvedAssemblies[args.Name] = assembly;
 
@@ -172,7 +180,7 @@ private Assembly OnResolve(object sender, AssemblyResolveEventArgs args)
                         }
                         catch (FileLoadException ex)
                         {
-                            EqtTrace.Info("AssemblyResolver.OnResolve: {0}: Failed to load assembly. Reason:{1} ", args.Name, ex);
+                            EqtTrace.Error("AssemblyResolver.OnResolve: {0}: Failed to load assembly. Reason:{1} ", args.Name, ex);
 
                             // Re-throw FileLoadException, because this exception means that the assembly
                             // was found, but could not be loaded. This will allow us to report a more