use some NotNullWhen on TryGets (#4520)

Author: SimonCropp

src/Microsoft.TestPlatform.Common/DataCollection/DataCollectionManager.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
 
@@ -387,7 +388,7 @@ private void CleanupPlugins()
     /// <param name="friendlyName">The friendly Name.</param>
     /// <param name="dataCollectorUri">The data collector Uri.</param>
     /// <returns><see cref="bool"/></returns>
-    protected virtual bool TryGetUriFromFriendlyName(string? friendlyName, out string? dataCollectorUri)
+    protected virtual bool TryGetUriFromFriendlyName(string? friendlyName, [NotNullWhen(true)] out string? dataCollectorUri)
     {
         TPDebug.Assert(_dataCollectorExtensionManager is not null, "_dataCollectorExtensionManager is null");
         foreach (var extension in _dataCollectorExtensionManager.TestExtensions)

src/Microsoft.TestPlatform.CoreUtilities/Helpers/DotnetHostHelper.cs

@@ -96,14 +96,13 @@ public string GetMonoPath()
         return monoPath;
     }
 
-    private bool TryGetExecutablePath(string executableBaseName, out string executablePath)
+    private bool TryGetExecutablePath(string executableBaseName, [NotNullWhen(true)] out string? executablePath)
     {
         if (_environment.OperatingSystem.Equals(PlatformOperatingSystem.Windows))
         {
             executableBaseName += ".exe";
         }
 
-        executablePath = string.Empty;
         var pathString = Environment.GetEnvironmentVariable("PATH")!;
         foreach (string path in pathString.Split(Path.PathSeparator))
         {
@@ -115,6 +114,7 @@ private bool TryGetExecutablePath(string executableBaseName, out string executab
             }
         }
 
+        executablePath = null;
         return false;
     }
 

src/Microsoft.TestPlatform.CrossPlatEngine/Client/TestLoggerManager.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -387,7 +388,7 @@ internal bool InitializeLoggerByUri(Uri uri, Dictionary<string, string?>? parame
     /// <param name="friendlyName">The friendly Name.</param>
     /// <param name="loggerUri">The logger Uri.</param>
     /// <returns><see cref="bool"/></returns>
-    internal bool TryGetUriFromFriendlyName(string? friendlyName, out Uri? loggerUri)
+    internal bool TryGetUriFromFriendlyName(string? friendlyName, [NotNullWhen(true)] out Uri? loggerUri)
     {
         var extensionManager = TestLoggerExtensionManager;
         foreach (var extension in extensionManager.TestExtensions)