refactor(core): rename ngInjectableDef to ɵprov (#33151)

Injectable defs are not considered public API, so the property
that contains them should be prefixed with Angular's marker
for "private" ('ɵ') to discourage apps from relying on def
APIs directly.

This commit adds the prefix and shortens the name from
ngInjectableDef to "prov" (for "provider", since injector defs
are known as "inj"). This is because property names cannot
be minified by Uglify without turning on property mangling
(which most apps have turned off) and are thus size-sensitive.

PR Close #33151

packages/core/src/change_detection/differs/iterable_differs.ts

@@ -143,7 +143,7 @@ export interface IterableDifferFactory {
  */
 export class IterableDiffers {
   /** @nocollapse */
-  static ngInjectableDef = ɵɵdefineInjectable({
+  static ɵprov = ɵɵdefineInjectable({
     token: IterableDiffers,
     providedIn: 'root',
     factory: () => new IterableDiffers([new DefaultIterableDifferFactory()])

packages/core/src/change_detection/differs/keyvalue_differs.ts

@@ -118,7 +118,7 @@ export interface KeyValueDifferFactory {
  */
 export class KeyValueDiffers {
   /** @nocollapse */
-  static ngInjectableDef = ɵɵdefineInjectable({
+  static ɵprov = ɵɵdefineInjectable({
     token: KeyValueDiffers,
     providedIn: 'root',
     factory: () => new KeyValueDiffers([new DefaultKeyValueDifferFactory()])