Allow ByRef return types in Dynamic Method (#15106)

* Allow ByRef return types in Dynamic Method

* Additional cleanup

Author: Alex

src/mscorlib/Resources/Strings.resx

@@ -413,7 +413,7 @@
     <value>Search pattern '{0}' cannot contain ".." to move up directories and can be contained only internally in file/directory names, as in "a..b".</value>
   </data>
   <data name="Arg_InvalidTypeInRetType" xml:space="preserve">
-    <value>The return Type contains some invalid type (i.e. null, ByRef)</value>
+    <value>The return Type must be a type provided by the runtime.</value>
   </data>
   <data name="Arg_InvalidTypeInSignature" xml:space="preserve">
     <value>The signature Type array contains some invalid type (i.e. null, void)</value>
@@ -3685,7 +3685,7 @@
   <data name="NotSupported_SignatureType" xml:space="preserve">
     <value>This method is not supported on signature types.</value>
   </data>
-    <data name="Memory_ThrowIfDisposed" xml:space="preserve">
+  <data name="Memory_ThrowIfDisposed" xml:space="preserve">
     <value>Memory&lt;T&gt; has been disposed.</value>
   </data>
   <data name="Memory_OutstandingReferences" xml:space="preserve">
@@ -3700,4 +3700,4 @@
   <data name="Arg_TypeNotSupported" xml:space="preserve">
     <value>Specified type is not supported</value>
   </data>
-</root>
+</root>

src/mscorlib/src/System/Reflection/Emit/DynamicMethod.cs

@@ -286,7 +286,7 @@ private unsafe void Init(String name,
                     if (signature[i] == null)
                         throw new ArgumentException(SR.Arg_InvalidTypeInSignature);
                     m_parameterTypes[i] = signature[i].UnderlyingSystemType as RuntimeType;
-                    if (m_parameterTypes[i] == null || !(m_parameterTypes[i] is RuntimeType) || m_parameterTypes[i] == (RuntimeType)typeof(void))
+                    if (m_parameterTypes[i] == null || m_parameterTypes[i] == (RuntimeType)typeof(void))
                         throw new ArgumentException(SR.Arg_InvalidTypeInSignature);
                 }
             }
@@ -297,7 +297,7 @@ private unsafe void Init(String name,
 
             // check and store the return value
             m_returnType = (returnType == null) ? (RuntimeType)typeof(void) : returnType.UnderlyingSystemType as RuntimeType;
-            if ((m_returnType == null) || !(m_returnType is RuntimeType) || m_returnType.IsByRef)
+            if (m_returnType == null)
                 throw new NotSupportedException(SR.Arg_InvalidTypeInRetType);
 
             if (transparentMethod)