Resubmit: Set wrappedMethod on getters/setters

[fatso83]

This is a re-submit of #2251 100% made by @rgroothuijsen, rebased on master. See it for background and discussion. Includes a revert of #2270. The original PR body is below:

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Purpose

This PR fixes #2198 by wrapping accessors if they are present, rather than the property they belong to.

Background

Because the current wrapMethod implementation only assumes the presence of a single method on a property, trying to set both a getter and a setter will cause the former to be overwritten by the latter, and not added as separate get and set methods. Furthermore, restore() is implemented on the property itself, which does not allow the spy.get.restore() and spy.set.restore() outlined in the documentation.

Solution

This problem was addressed by changing wrapMethod to handle multiple methods per property. This includes a check whether any particular method is an accessor or not, and a method-wrapping implementation is chosen based on this. If the method in question is not a "get" or "set" method, the existing implementation will be used.

In order to satisfy ESLint code quality requirements, some restructuring of wrapMethod has been performed as well. To the extent possible, however, the existing structure has been left alone.

• restore() was moved because function declarations are not allowed inside a loop
• Parts of the code have been separated into functions because the complexity of wrapMethod had become too high

How to verify

1. Check out this branch
2. npm install
3. npm test (See included test for details)