Cleanup how code is executed in our unit tests (#78112)

As part of #78024 I needed to change how output was handled by our unit
tests. In looking at the test execution code I noticed that it was in
need of a bit of a cleanup. The responsibilities of the layers was not
clear and this lead to a lot of code duplication as well as subtle
behavior differences between .NET Core and Framework. This change does
the following:

- Changes the responsibility of `IRuntimeEnvironment` to be _only_ about
how code is executed. No more emitting code, calling into `Assert`, etc
... This is just about running code in a specific environment.
- Moves the responsibility of verifying the output is as expected to
`CompilationVerifier`
- Moves the responsibility of emitting the code to be
`CompilationVerifier`
- Enables NRT in several places to better track how `null` is handled.
There is so much implicit `null` usage in the low test layers that it
was making the hard to follow. Decided to just turn on NRT there and
work through the problems.

Author: arunchndr

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenLockTests.cs

@@ -1771,7 +1771,7 @@ public void Write(T newItem)
 
             item = newItem;
             empty = false;
-            Console.Error.WriteLine(""{0} wrote {1}"", Thread.CurrentThread.Name, newItem);
+            Console.WriteLine(""{0} wrote {1}"", Thread.CurrentThread.Name, newItem);
             Monitor.PulseAll(bufferLock);
         }
     }
@@ -1784,7 +1784,7 @@ public T Read()
 
             empty = true;
             T result = item;
-            Console.Error.WriteLine(""{0} read {1}"", Thread.CurrentThread.Name, result);
+            Console.WriteLine(""{0} read {1}"", Thread.CurrentThread.Name, result);
             Monitor.PulseAll(bufferLock);
             return result;
         }

src/Compilers/CSharp/Test/Symbol/Symbols/CSharpCompilerFeatureRequiredTests.cs

@@ -50,7 +50,7 @@ protected override CSharpTestSource GetUsage() => """
         _ = new OnThisIndexerParameter()[1];
         """;
 
-    internal override string VisualizeRealIL(IModuleSymbol peModule, CompilationTestData.MethodData methodData, IReadOnlyDictionary<int, string> markers, bool areLocalsZeroed)
+    internal override string VisualizeRealIL(IModuleSymbol peModule, CompilationTestData.MethodData methodData, IReadOnlyDictionary<int, string>? markers, bool areLocalsZeroed)
     {
         return _csharpTest.VisualizeRealIL(peModule, methodData, markers, areLocalsZeroed);
     }

src/Compilers/CSharp/Test/Symbol/Symbols/FunctionPointerTypeSymbolTests.cs

@@ -1165,6 +1165,7 @@ unsafe void M()
             Assert.NotNull(a);
             Assert.Equal("System.Int32 a", a.ToTestDisplayString());
 
+            Assert.NotNull(functionPointerTypeSyntax.Parent);
             VerifyOperationTreeForNode(comp, model, functionPointerTypeSyntax.Parent, expectedOperationTree: @"
 IVariableDeclarationOperation (1 declarators) (OperationKind.VariableDeclaration, Type: null, IsInvalid) (Syntax: 'delegate*<int[a]> local')
   Ignored Dimensions(1):
@@ -1271,6 +1272,7 @@ unsafe void M()
             Assert.Equal("C.D", nestedTypeInfo.Type!.ToTestDisplayString());
             Assert.False(nestedTypeInfo.Type!.IsErrorType());
 
+            Assert.NotNull(functionPointerTypeSyntax.Parent);
             VerifyOperationTreeForNode(comp, model, functionPointerTypeSyntax.Parent, expectedOperationTree: @"
 IVariableDeclarationOperation (1 declarators) (OperationKind.VariableDeclaration, Type: null, IsInvalid) (Syntax: 'delegate*<C.D> d')
   Declarators:

src/Compilers/Core/CodeAnalysisTest/Symbols/DocumentationCommentIdTests.cs

@@ -186,7 +186,7 @@ unsafe void M({{type}} i)
         }
 
         internal override string VisualizeRealIL(
-            IModuleSymbol peModule, CompilationTestData.MethodData methodData, IReadOnlyDictionary<int, string> markers, bool areLocalsZeroed)
+            IModuleSymbol peModule, CompilationTestData.MethodData methodData, IReadOnlyDictionary<int, string>? markers, bool areLocalsZeroed)
             => throw new NotImplementedException();
     }
 }