Ember's implicit injections feature is removed in Ember 4.x. We want to give ourselves more time to migrate to explicit injections, so this commit re-implements our implicit injections as extensions to the base framework classes.
Incremental migration to newer patterns can be achieved using the `@disableImplicitInjections` class decorator (available from `discourse/lib/implicit-injections').
This resolves and unsilences the `implicit-injections` deprecation.