Improve quick info display on properties belonging to all union contextual type members (#56088)

Author: Andarist

src/services/services.ts

@@ -3282,7 +3282,9 @@ export function getPropertySymbolsFromContextualType(node: ObjectLiteralElementW
         // Bad discriminant -- do again without discriminating
         return mapDefined(contextualType.types, t => t.getProperty(name));
     }
-    return discriminatedPropertySymbols;
+    // by eliminating duplicates we might even end up with a single symbol
+    // that helps with displaying better quick infos on properties of union types
+    return deduplicate(discriminatedPropertySymbols, equateValues);
 }
 
 function isArgumentOfElementAccessExpression(node: Node) {

tests/cases/fourslash/quickInfoJsDocNonDiscriminatedUnionSharedProp.ts

@@ -0,0 +1,45 @@
+/// <reference path='fourslash.ts'/>
+
+//// interface Entries {
+////   /**
+////    * Plugins info...
+////    */
+////   plugins?: Record<string, Record<string, unknown>>;
+////   /**
+////    * Output info...
+////    */
+////   output?: string;
+////   /**
+////    * Format info...
+////    */
+////   format?: string;
+//// }
+////
+//// interface Input extends Entries {
+////   /**
+////    * Input info...
+////    */
+////   input: string;
+//// }
+////
+//// interface Types extends Entries {
+////   /**
+////    * Types info...
+////    */
+////   types: string;
+//// }
+////
+//// type EntriesOptions = Input | Types;
+////
+//// const options: EntriesOptions[] = [
+////   {
+////     input: "./src/index.ts",
+////     /*1*/output: "./dist/index.mjs",
+////   },
+////   {
+////     types: "./src/types.ts",
+////     format: "esm",
+////   },
+//// ];
+
+verify.quickInfoAt("1", "(property) Entries.output?: string", "Output info...");