Addresses issue absinthe-graphql#1149.
module `Absinthe.Phase.Document.Execution.Resolution` walks the result
tree and tracks `path` using a function parameter. At the same time, a
`Resolution` struct is passed, which `path` field is not consistently
tracked.

The problem manifests itself in bogus Resolution path passed onto
`resolve_type` function as described in function absinthe-graphql#1149.

The reason for not updating the resolution.path in the walk process can
be explained by comment of @benwilson512: `Traditionally the reason we
pass in the env has more to do with making the schema available and the
context available, I don't know that the other values in that struct
have been validated in this situation.` Perhaps path parameter was used
in the beginning and later resolution paramter was added, but not used
to track current tree walk in it's path field.

Nevertheless, the resolution is passed on to user code - into
`resolve_type(value, resolution)` callback, which might use path to
understand the context of value (eg. what is the type of parent?).

This PR fixes the bookkeeping of `resolution.path` field. I have not
inspected the use of other field, I am not sure which ones would change
during the value walk (`parent_type` maybe?).

One could consider to just use `resolution.path` instead of `path`
parameter - so there is not double bookkeeping of this value. This is up
to maintainers to decide, I did not make such a change.