add error showing where prop was also declared if is a dup

Author: collin5

src/compiler/checker.ts

@@ -6289,7 +6289,7 @@ namespace ts {
                         // report an error at each declaration.
                         const declarations = earlySymbol ? concatenate(earlySymbol.declarations, lateSymbol.declarations) : lateSymbol.declarations;
                         const name = (<LiteralType>type).value || declarationNameToString(decl.name);
-                        forEach(declarations, declaration => error(getNameOfDeclaration(declaration) || declaration, Diagnostics.Duplicate_property_0, name));
+                        forEach(declarations, declaration => error(getNameOfDeclaration(declaration) || declaration, Diagnostics.Property_0_was_also_declared_here, name));
                         error(decl.name || decl, Diagnostics.Duplicate_property_0, name);
                         lateSymbol = createSymbol(SymbolFlags.None, memberName, CheckFlags.Late);
                     }

src/compiler/diagnosticMessages.json

@@ -2485,6 +2485,10 @@
         "category": "Error",
         "code": 2732
     },
+    "Property '{0}' was also declared here.": {
+        "category": "Error",
+        "code": 2733
+    },
     "It is highly likely that you are missing a semicolon.": {
         "category": "Error",
         "code": 2734

tests/baselines/reference/dynamicNamesErrors.errors.txt

@@ -1,5 +1,5 @@
 tests/cases/compiler/dynamicNamesErrors.ts(5,5): error TS2718: Duplicate property '1'.
-tests/cases/compiler/dynamicNamesErrors.ts(6,5): error TS2718: Duplicate property '1'.
+tests/cases/compiler/dynamicNamesErrors.ts(6,5): error TS2733: Property '1' was also declared here.
 tests/cases/compiler/dynamicNamesErrors.ts(19,5): error TS2717: Subsequent property declarations must have the same type.  Property '[c1]' must be of type 'number', but here has type 'string'.
 tests/cases/compiler/dynamicNamesErrors.ts(24,1): error TS2322: Type 'T2' is not assignable to type 'T1'.
   Types of property '[c0]' are incompatible.
@@ -19,7 +19,7 @@ tests/cases/compiler/dynamicNamesErrors.ts(25,1): error TS2322: Type 'T1' is not
 !!! error TS2718: Duplicate property '1'.
         1: number;
         ~
-!!! error TS2718: Duplicate property '1'.
+!!! error TS2733: Property '1' was also declared here.
     }
 
     interface T1 {