Add inject service RFC

text/0752-inject-service.md

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+---
+Stage: Accepted
+Start Date: 2021-06-10
+Release Date: Unreleased
+Release Versions:
+  ember-source: vX.Y.Z
+  ember-data: vX.Y.Z
+Relevant Team(s): Ember.js, Learning
+RFC PR: https://github.com/emberjs/rfcs/pull/752
+---
+
+<!--- 
+Directions for above: 
+
+Stage: Leave as is
+Start Date: Fill in with today's date, YYYY-MM-DD
+Release Date: Leave as is
+Release Versions: Leave as is
+Relevant Team(s): Fill this in with the [team(s)](README.md#relevant-teams) to which this RFC applies
+RFC PR: Fill this in with the URL for the Proposal RFC PR
+-->
+
+# Rename `inject` import to `service`
+
+## Summary
+
+Currently, in order to use a service in any framework class you can do it like this:
+
+```js
+import { inject } from '@ember/service';
+
+export class MyComponent extends Component {
+  @inject router;
+}
+```
+
+However, it is very common to actually alias this import to `service`, like this:
+
+```js
+import { inject as service } from '@ember/service';
+
+export class MyComponent extends Component {
+  @service router;
+}
+```
+
+This RFC proposes to actually provide this as a `service` import directly.
+
+
+## Motivation
+
+You cannot properly/easily use editor autocompletion to import `@service`. 
+
+Even in the guides, `inject` is aliased to `service` (see: https://guides.emberjs.com/release/services/#toc_accessing-services)
+
+Finally, there is also an `inject` export from `@ember/controller`, which is also a possible source of confusion.
+
+By exporting this directly as `service`, this would be streamlined:
+
+```js
+import { service } from '@ember/service';
+
+export class MyComponent extends Component {
+  @service router;
+}
+```
+
+## Detailed design
+
+We add an export `service` from the `@ember/service` package with the semantics
+of `inject`.
+
+Import of `inject` itself will be deprecated targeting Ember 5.0 for removal,
+and the app blueprint will be updated as soon as possible to the new API.
+
+Addons will likely want to support the legacy API for a long time, especially
+if the legacy API is not deprecated in Ember 4.0.0. The addon blueprint and
+best practice should be to:
+
+```js
+import * as ES from '@ember/service';
+const service = ES.service ?? ES.inject;
+```
+
+Then use `service` for injections.
+
+## How we teach this
+
+The docs should be updated to directly import `import { service } from '@ember/service';`.
+
+## Drawbacks
+
+It might be considered churn. However, we could probably provide a codemod to
+automatically rename the imports, lessening the churn.
+
+Addons will need to live with a degraded injection API for a long time, if they
+want to support both versions.
+
+## Alternatives
+
+We could leave the import as it is, continuing to suggest people rename the import to `service`. 
+
+Or we could stop suggesting the import and push for the community to simply use `@inject myService`.
+
+We could also choose a different name for the import (e.g. `injectService` or something like this).
+
+## Unresolved questions