Give a related span pointing to the implementation signature when reporting incompatibility.

Author: DanielRosenwasser

src/compiler/checker.ts

@@ -24448,7 +24448,10 @@ namespace ts {
                     const bodySignature = getSignatureFromDeclaration(bodyDeclaration);
                     for (const signature of signatures) {
                         if (!isImplementationCompatibleWithOverload(bodySignature, signature)) {
-                            error(signature.declaration, Diagnostics.This_overload_signature_is_not_compatible_with_its_implementation_signature);
+                            addRelatedInfo(
+                                error(signature.declaration, Diagnostics.This_overload_signature_is_not_compatible_with_its_implementation_signature),
+                                createDiagnosticForNode(bodyDeclaration, Diagnostics.The_implementation_signature_is_declared_here)
+                            );
                             break;
                         }
                     }

src/compiler/diagnosticMessages.json

@@ -2585,6 +2585,10 @@
         "category": "Error",
         "code": 2749
     },
+    "The implementation signature is declared here.": {
+        "category": "Error",
+        "code": 2750
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",