Fix #51437 Duplicate "Duplicate identifier" errors (#51594)

* retroactive approach to remove duplicate diagnostics

* use code instead of messageText, update test

* use existing de-dupe function

* rename test and baselines

* add fourslash test for better assertion of fix

* review feedback: move deduplicate to getDiagnosticsHelper

* accept baseline with sorted diagnostics

* remove newline

src/compiler/program.ts

@@ -2639,7 +2639,7 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
         getDiagnostics: (sourceFile: SourceFile, cancellationToken: CancellationToken | undefined) => readonly T[],
         cancellationToken: CancellationToken | undefined): readonly T[] {
         if (sourceFile) {
-            return getDiagnostics(sourceFile, cancellationToken);
+            return sortAndDeduplicateDiagnostics(getDiagnostics(sourceFile, cancellationToken));
         }
         return sortAndDeduplicateDiagnostics(flatMap(program.getSourceFiles(), sourceFile => {
             if (cancellationToken) {

tests/baselines/reference/tsserver/projects/handles-the-missing-files-added-with-tripleslash-ref.js

@@ -118,19 +118,6 @@ FsWatchesRecursive::
 Info 15   [00:00:34.000] response:
     {
       "response": [
-        {
-          "start": {
-            "line": 2,
-            "offset": 29
-          },
-          "end": {
-            "line": 2,
-            "offset": 30
-          },
-          "text": "Cannot find name 'y'.",
-          "code": 2304,
-          "category": "error"
-        },
         {
           "start": {
             "line": 1,
@@ -143,6 +130,19 @@ Info 15   [00:00:34.000] response:
           "text": "File '/a/b/commonFile2.ts' not found.",
           "code": 6053,
           "category": "error"
+        },
+        {
+          "start": {
+            "line": 2,
+            "offset": 29
+          },
+          "end": {
+            "line": 2,
+            "offset": 30
+          },
+          "text": "Cannot find name 'y'.",
+          "code": 2304,
+          "category": "error"
         }
       ],
       "responseRequired": true

tests/cases/fourslash/codeFixInferFromUsageMultipleParametersJS.ts

@@ -11,7 +11,7 @@
 
 verify.codeFix({
     description: "Infer parameter types from usage",
-    index: 4,
+    index: 3,
     newFileContent:
 `/**
  * @param {number} a

tests/cases/fourslash/deduplicateDuplicateMergedBindCheckErrors.ts

@@ -0,0 +1,12 @@
+/// <reference path="./fourslash.ts" />
+
+//// class X {
+////   foo() {
+////       return 1;
+////   }
+////   get foo() {
+////       return 1;
+////   }
+//// }
+
+verify.numberOfErrorsInCurrentFile(2);