[WIP] [RFC] Allow sequence to be composed from actions with class/method dependency injection

[raymondfeng]

The PR adds the ability to declare action classes/methods and utilizes dependencies to create a sequence of actions.

• Add @action to decorate action classes and methods and use corresponding metadata to determine the order of invocation so that we can build a sequence.

• Add invokeMethod to invoke a prototype method of a given class with dependency injection

Description

• https://github.com/strongloop/loopback-next/blob/c4051416eb0d7dc1ac249557819885700519927d/packages/context/test/acceptance/method-level-bindings.feature.md
• https://github.com/strongloop/loopback-next/blob/c4051416eb0d7dc1ac249557819885700519927d/packages/core/test/acceptance/action-composition.feature.md

Connect to #139

Checklist

• New tests added or existing tests modified to cover all changes
• Code conforms with the style
  guide

[bajtos]

There have been no updates in this pull request for many months, I am closing it for now. @raymondfeng feel free to reopen if you get time to continue this work. (Considering how outdated these changes are, it may be better to start from scratch.)