Flag JS Literals and ignore assignments/accesses to invalid props, instead of adding an index (#25996)

* Remove index signatures from js literals, use an object flag to indicate errors should be ignored instead

* Add focused test on the keyof problem

* Fix fourslash test

* Reenable errors with noImplicitAny flag

* Also disable excess property checks outside of noImplicitAny mode for js literals

* Edit and move comments

tests/cases/compiler/checkJsObjectLiteralHasCheckedKeyof.ts

@@ -0,0 +1,14 @@
+// @allowJs: true
+// @outDir: ./out
+// @filename: file.js
+// @ts-check
+const obj = {
+    x: 1,
+    y: 2
+};
+
+/**
+ * @type {keyof typeof obj}
+ */
+let selected = "x";
+selected = "z"; // should fail

tests/cases/fourslash/codeFixUndeclaredAcrossFiles1.ts

@@ -28,7 +28,7 @@ verify.rangeIs(`
     m2(c: C): any {
         throw new Error("Method not implemented.");
     }
-    y: { [x: string]: any; };
+    y: {};
     m1(): any {
         throw new Error("Method not implemented.");
     }