[DependencyInjection] added support for inlining Configurators

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This is one commit from #9432.

As mentioned in #3758 configurators can not be private (it's just ignored). This pull changes that and allows them to be inlined. It it also creates better code if a configurator is used multiple times for one service (i.e. to both inject it and configure the same service, or to configure multiple inlined services) but this should be very rare.