Add a testcase that fails when someone tried to make an Object.keys PR (microsoft#44368)

Author: RyanCavanaugh

tests/baselines/reference/noObjectKeysToKeyofT.js

@@ -0,0 +1,14 @@
+//// [noObjectKeysToKeyofT.ts]
+// Do not change Object.keys to return keyof T.
+// The current return type (string[]) is intentional.
+Object.keys({ a: 0 }).push("b");
+
+// See also
+// https://stackoverflow.com/questions/55012174/why-doesnt-object-keys-return-a-keyof-type-in-typescript
+
+//// [noObjectKeysToKeyofT.js]
+// Do not change Object.keys to return keyof T.
+// The current return type (string[]) is intentional.
+Object.keys({ a: 0 }).push("b");
+// See also
+// https://stackoverflow.com/questions/55012174/why-doesnt-object-keys-return-a-keyof-type-in-typescript

tests/baselines/reference/noObjectKeysToKeyofT.symbols

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/noObjectKeysToKeyofT.ts ===
+// Do not change Object.keys to return keyof T.
+// The current return type (string[]) is intentional.
+Object.keys({ a: 0 }).push("b");
+>Object.keys({ a: 0 }).push : Symbol(Array.push, Decl(lib.es5.d.ts, --, --))
+>Object.keys : Symbol(ObjectConstructor.keys, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>keys : Symbol(ObjectConstructor.keys, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
+>a : Symbol(a, Decl(noObjectKeysToKeyofT.ts, 2, 13))
+>push : Symbol(Array.push, Decl(lib.es5.d.ts, --, --))
+
+// See also
+// https://stackoverflow.com/questions/55012174/why-doesnt-object-keys-return-a-keyof-type-in-typescript

tests/baselines/reference/noObjectKeysToKeyofT.types

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/noObjectKeysToKeyofT.ts ===
+// Do not change Object.keys to return keyof T.
+// The current return type (string[]) is intentional.
+Object.keys({ a: 0 }).push("b");
+>Object.keys({ a: 0 }).push("b") : number
+>Object.keys({ a: 0 }).push : (...items: string[]) => number
+>Object.keys({ a: 0 }) : string[]
+>Object.keys : { (o: object): string[]; (o: {}): string[]; }
+>Object : ObjectConstructor
+>keys : { (o: object): string[]; (o: {}): string[]; }
+>{ a: 0 } : { a: number; }
+>a : number
+>0 : 0
+>push : (...items: string[]) => number
+>"b" : "b"
+
+// See also
+// https://stackoverflow.com/questions/55012174/why-doesnt-object-keys-return-a-keyof-type-in-typescript

tests/cases/compiler/noObjectKeysToKeyofT.ts

@@ -0,0 +1,8 @@
+// @target: es2016
+
+// Do not change Object.keys to return keyof T.
+// The current return type (string[]) is intentional.
+Object.keys({ a: 0 }).push("b");
+
+// See also
+// https://stackoverflow.com/questions/55012174/why-doesnt-object-keys-return-a-keyof-type-in-typescript