Move SourceOrdinaryMethodSymbol functionality that is not syntax specific into...

Move SourceOrdinaryMethodSymbol functionality that is not syntax specific into a new base class. (#45424)

This work is related to #45296.

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberMethodSymbol.cs

@@ -923,7 +923,7 @@ internal override void AddSynthesizedAttributes(PEModuleBuilder moduleBuilder, r
         /// Checks to see if a body is legal given the current modifiers.
         /// If it is not, a diagnostic is added with the current type.
         /// </summary>
-        protected void CheckModifiersForBody(SyntaxNode declarationSyntax, Location location, DiagnosticBag diagnostics)
+        protected void CheckModifiersForBody(Location location, DiagnosticBag diagnostics)
         {
             if (IsExtern && !IsAbstract)
             {

src/Compilers/CSharp/Portable/Symbols/Source/SourcePropertyAccessorSymbol.cs

@@ -174,7 +174,7 @@ internal sealed override ImmutableArray<string> NotNullWhenFalseMembers
                 isMetadataVirtualIgnoringModifiers: explicitInterfaceImplementations.Any());
 
             CheckFeatureAvailabilityAndRuntimeSupport(syntax, location, hasBody: true, diagnostics: diagnostics);
-            CheckModifiersForBody(syntax, location, diagnostics);
+            CheckModifiersForBody(location, diagnostics);
 
             var info = ModifierUtils.CheckAccessibility(this.DeclarationModifiers, this, isExplicitInterfaceImplementation);
             if (info != null)
@@ -248,7 +248,7 @@ internal sealed override ImmutableArray<string> NotNullWhenFalseMembers
 
             if (hasBody || hasExpressionBody)
             {
-                CheckModifiersForBody(syntax, location, diagnostics);
+                CheckModifiersForBody(location, diagnostics);
             }
 
             var info = ModifierUtils.CheckAccessibility(this.DeclarationModifiers, this, isExplicitInterfaceImplementation);