Move @ember/polyfill types to stable

The updated types and tests now match those of `Object.assign`

toward #19946

packages/@ember/polyfills/lib/assign.ts

@@ -7,7 +7,7 @@ import { deprecate } from '@ember/debug';
 export function assign<T, U>(target: T, source: U): T & U;
 export function assign<T, U, V>(target: T, source1: U, source2: V): T & U & V;
 export function assign<T, U, V, W>(target: T, source1: U, source2: V, source3: W): T & U & V & W;
-export function assign(target: object, ...sources: object[]): object;
+export function assign(target: object, ...sources: any[]): any;
 /**
   Copy properties from a source object to a target object. Source arguments remain unchanged.
 
@@ -29,7 +29,7 @@ export function assign(target: object, ...sources: object[]): object;
   @public
   @static
 */
-export function assign(target: object, ...rest: object[]): object {
+export function assign(target: object, ...sources: any[]): any {
   deprecate(
     'Use of `assign` has been deprecated. Please use `Object.assign` or the spread operator instead.',
     false,
@@ -45,5 +45,5 @@ export function assign(target: object, ...rest: object[]): object {
     }
   );
 
-  return Object.assign(target, ...rest);
+  return Object.assign(target, ...sources);
 }

type-tests/@ember/polyfills-tests.ts

@@ -5,19 +5,19 @@ import { expectTypeOf } from 'expect-type';
   /* assign */
   assign({}, { a: 'b' });
   expectTypeOf(assign({}, { a: 'b' }).a).toBeString();
-  expectTypeOf(assign({ a: 6 }, { a: 'b' }).a).toBeString();
+  expectTypeOf(assign({ a: 6 }, { a: 'b' }).a).toEqualTypeOf<string & number>();
   expectTypeOf(assign({ a: 6 }, {}).a).toBeNumber();
   // @ts-expect-error
   assign({ b: 6 }, {}).a;
   expectTypeOf(assign({}, { b: 6 }, {}).b).toBeNumber();
   expectTypeOf(assign({ a: 'hello' }, { b: 6 }, {}).a).toBeString();
-  expectTypeOf(assign({ a: 'hello' }, { b: 6 }, { a: true }).a).toBeBoolean();
+  // @ts-expect-error
+  assign({ a: 'hello' }, { b: 6 }, { a: true }).a;
   // @ts-expect-error
   assign({ a: 'hello' }, '', { a: true }).a;
   expectTypeOf(
-    assign({ d: ['gobias industries'] }, { a: 'hello' }, { b: 6 }, { a: true }).d
+    assign({ d: ['gobias industries'] }, { a: 'hello' }, { b: 6 }).d
   ).toEqualTypeOf<string[]>();
-  // @ts-expect-error
   assign({}, { a: 0 }, { b: 1 }, { c: 2 }, { d: 3 }).a;
 
   // matches Object.assign

types/preview/index.d.ts

@@ -89,9 +89,6 @@ import './@ember/object/observers';
 import './@ember/object/promise-proxy-mixin';
 import './@ember/object/proxy';
 
-import './@ember/polyfills';
-import './@ember/polyfills/types';
-
 import './@ember/routing';
 import './@ember/routing/-private/router-dsl';
 import './@ember/routing/auto-location';

types/publish.mjs

@@ -254,8 +254,6 @@ const PREVIEW_MODULES = [
   '@ember/object/observers.d.ts',
   '@ember/object/promise-proxy-mixin.d.ts',
   '@ember/object/proxy.d.ts',
-  '@ember/polyfills/index.d.ts',
-  '@ember/polyfills/lib/assign.d.ts',
   '@ember/renderer/index.d.ts',
   '@ember/routing/-internals.d.ts',
   '@ember/routing/auto-location.d.ts',