Function deepMergeWithResolver

deepMergeWithResolver(a: object, b: object, resolver: function): object
Creates a new object by merging object b onto object a, biased toward b:
- Fields in b that don't exist in a are created.
- Fields in a that don't exist in b are left unchanged.
- Fields in a and b are passed as arguments to the resolve function (a,b) and its return assigns the new value.
Parameters
- a: object
  The base object.
- b: object
  The overriding object.
- resolver: function
  The resolver function.
Returns object
A new merged object.

Throws
If either a or b is not a plain object.