refactor(ivy): make return value of define(Component|Directive|Pipe|Injector|Injectable) private (#23371)

Ivy definition looks something like this:

```
class MyService {
  static ngInjectableDef = defineInjectable({
    …
  });
}
```

Here the argument to `defineInjectable` is well known public contract which needs
to be honored in backward compatible way between versions. The type of the
return value of `defineInjectable` on the other hand is private and can change
shape drastically between versions without effecting backwards compatibility of
libraries publish to NPM. To our users it is effectively an `OpaqueToken`.

By prefixing the type with `ɵ` we are communicating the the outside world that
the value is not public API and is subject to change without backward compatibility.

PR Close #23371

packages/core/test/bundling/injection/usage.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {InjectableDef, Injector, InjectorDef, createInjector, defineInjectable, defineInjector} from '@angular/core';
+import {Injector, createInjector, defineInjectable, defineInjector, ɵInjectableDef, ɵInjectorDef} from '@angular/core';
 
 export class RootService {
   static ngInjectableDef = defineInjectable({