`vue/no-unused-properties` should handle `inject`

<!-- Before proposing rule changes, please make sure it hasn't been posted already. You can see all open propositions here: https://github.com/vuejs/eslint-plugin-vue/issues?q=is%3Aopen+is%3Aissue+label%3A%22new+rule+proposition%22 --> **What rule do you want to change?** [vue/no-unused-properties](https://eslint.vuejs.org/rules/no-unused-properties) **Does this change cause the rule to produce more or fewer warnings?** More. **How will the change be implemented? (New option, new default behavior, etc.)?** Allow `inject` as a new element in `groups`. **Please provide some example code that this change will affect:** <!-- Put your code examples here --> ```vue <script> export default { inject: ['unused'], }; </script> ``` **What does the rule currently do for this code?** Nothing. **What will the rule do after it's changed?** `warning 'unused' of inject found, but never used vue/no-unused-properties` **Additional context** n/a <!-- Add any other context or screenshots about the feature request here. -->