A class that is provided as Angular service is required to have an
`@Injectable()` decorator so that the compiler generates its injectable
definition for the runtime. Applications are automatically migrated
using the "missing-injectable" schematic, however libraries built for
older version of Angular may not yet satisfy this requirement.
This commit ports the "missing-injectable" schematic to a migration that
is ran when ngcc is processing a library. This ensures that any service
that is provided from an NgModule or Directive/Component will have an
`@Injectable()` decorator.
PR Close#33362
