Enhance error message for multiple constructors

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

@@ -1727,7 +1727,8 @@ private void ReportMethodSignatureCollision(DiagnosticBag diagnostics, SourceMem
             // Special case: if there are two destructors, use the destructor syntax instead of "Finalize"
             var methodName = (method1.MethodKind == MethodKind.Destructor && method2.MethodKind == MethodKind.Destructor) ?
                 "~" + this.Name :
-                method1.Name;
+                (method1.IsConstructor() ? this.Name : method1.Name);
+
             // Type '{1}' already defines a member called '{0}' with the same parameter types
             diagnostics.Add(ErrorCode.ERR_MemberAlreadyExists, method1.Locations[0], methodName, this);
         }

src/Compilers/CSharp/Test/Semantic/Semantics/RecordTests.cs

@@ -608,9 +608,9 @@ public static void Main()
 }";
             var comp = CreateCompilation(src);
             comp.VerifyDiagnostics(
-                // (5,12): error CS0111: Type 'C' already defines a member called '.ctor' with the same parameter types
+                // (5,12): error CS0111: Type 'C' already defines a member called 'C' with the same parameter types
                 //     public C(int a, int b)
-                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments(".ctor", "C").WithLocation(5, 12),
+                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments("C", "C").WithLocation(5, 12),
                 // (5,12): error CS8862: A constructor declared in a record with parameters must have 'this' constructor initializer.
                 //     public C(int a, int b)
                 Diagnostic(ErrorCode.ERR_UnexpectedOrMissingConstructorInitializerInRecord, "C").WithLocation(5, 12),

src/Compilers/CSharp/Test/Symbol/Compilation/GetSemanticInfoTests.cs

@@ -5822,12 +5822,12 @@ partial class C
             model1.GetDeclarationDiagnostics().Verify();
 
             model2.GetDeclarationDiagnostics().Verify(
-                // (4,5): error CS0111: Type 'C' already defines a member called '.ctor' with the same parameter types
-                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments(".ctor", "C").WithLocation(4, 5));
+                // (4,5): error CS0111: Type 'C' already defines a member called 'C' with the same parameter types
+                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments("C", "C").WithLocation(4, 5));
 
             model3.GetDeclarationDiagnostics().Verify(
-                // (4,5): error CS0111: Type 'C' already defines a member called '.ctor' with the same parameter types
-                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments(".ctor", "C").WithLocation(4, 5));
+                // (4,5): error CS0111: Type 'C' already defines a member called 'C' with the same parameter types
+                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments("C", "C").WithLocation(4, 5));
 
             Assert.Equal(3, comp.GlobalNamespace.GetMember<NamedTypeSymbol>("C").InstanceConstructors.Length);
         }

src/Compilers/CSharp/Test/Symbol/Symbols/Source/RecordTests.cs

@@ -74,9 +74,9 @@ public C(int a, string b)
     }
 }");
             comp.VerifyDiagnostics(
-                // (4,12): error CS0111: Type 'C' already defines a member called '.ctor' with the same parameter types
+                // (4,12): error CS0111: Type 'C' already defines a member called 'C' with the same parameter types
                 //     public C(int a, string b)
-                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments(".ctor", "C").WithLocation(4, 12),
+                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "C").WithArguments("C", "C").WithLocation(4, 12),
                 // (4,12): error CS8862: A constructor declared in a record with parameters must have 'this' constructor initializer.
                 //     public C(int a, string b)
                 Diagnostic(ErrorCode.ERR_UnexpectedOrMissingConstructorInitializerInRecord, "C").WithLocation(4, 12)