Fix null warnings (#22615)

Author: BrennanConroy

src/Shared/Shared.sln

@@ -1,10 +1,12 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 16
+# Visual Studio Version 16
 VisualStudioVersion = 16.0.0.0
 MinimumVisualStudioVersion = 16.0.0.0
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.AspNetCore.Shared.Tests", "test\Shared.Tests\Microsoft.AspNetCore.Shared.Tests.csproj", "{06CD38EF-7733-4284-B3E4-825B6B63E1DD}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ThrowingLibrary", "test\testassets\ThrowingLibrary\ThrowingLibrary.csproj", "{4799E505-5F83-4AB3-B96D-EACEB3528854}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,6 +17,10 @@ Global
 		{06CD38EF-7733-4284-B3E4-825B6B63E1DD}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{06CD38EF-7733-4284-B3E4-825B6B63E1DD}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{06CD38EF-7733-4284-B3E4-825B6B63E1DD}.Release|Any CPU.Build.0 = Release|Any CPU
+		{4799E505-5F83-4AB3-B96D-EACEB3528854}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4799E505-5F83-4AB3-B96D-EACEB3528854}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4799E505-5F83-4AB3-B96D-EACEB3528854}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4799E505-5F83-4AB3-B96D-EACEB3528854}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/Shared/StackTrace/StackFrame/ParameterDisplayInfo.cs

@@ -1,17 +1,18 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Text;
+#nullable enable
 
 namespace Microsoft.Extensions.StackTrace.Sources
 {
     internal class ParameterDisplayInfo
     {
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
-        public string Type { get; set; }
+        public string? Type { get; set; }
 
-        public string Prefix { get; set; }
+        public string? Prefix { get; set; }
 
         public override string ToString()
         {

src/Shared/StackTrace/StackFrame/StackFrameInfo.cs

@@ -1,18 +1,19 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Diagnostics;
+#nullable enable
 
 namespace Microsoft.Extensions.StackTrace.Sources
 {
     internal class StackFrameInfo
     {
         public int LineNumber { get; set; }
 
-        public string FilePath { get; set; }
+        public string? FilePath { get; set; }
 
-        public StackFrame StackFrame { get; set; }
+        public StackFrame? StackFrame { get; set; }
 
-        public MethodDisplayInfo MethodDisplayInfo { get; set; }
+        public MethodDisplayInfo? MethodDisplayInfo { get; set; }
     }
 }

src/Shared/StackTrace/StackFrame/StackTraceHelper.cs

@@ -132,7 +132,7 @@ public static IList<StackFrameInfo> GetFrames(Exception exception, out Aggregate
                         parameterType = parameterType.GetElementType();
                     }
 
-                    parameterTypeString = TypeNameHelper.GetTypeDisplayName(parameterType, fullName: false, includeGenericParameterNames: true);
+                    parameterTypeString = TypeNameHelper.GetTypeDisplayName(parameterType!, fullName: false, includeGenericParameterNames: true);
                 }
 
                 return new ParameterDisplayInfo