BUGFIX: Use new typeMapping graphql API

[unclecheese]

Resolves #954

[unclecheese]

Merging ahead of green, because it is interdependent with this graphql fix and these tests can't possibly pass without a merge of one or the other

[emteknetnz]

@unclecheese please don't self merge unapproved pull-requests on stable branches. I'm less concerned about graphql4's master branch as it's non-stable, however elemental 4 is stable. The build for this PR ended up red and probably would not have been merged in its current state

[unclecheese]

That was exactly the issue, though. The build couldn't have possibly been green, because it needed that GraphQL PR merged. Now that elemental is in the GraphQL build matrix, these two PRs were interdependent, and something had to merge on red to unlock that paradox.

[emteknetnz]

I suppose its an unfortunate side-effect that the elemental 4 _graphql folder is effectively at a non-stable level despite it being within stable branch

[unclecheese]

Well the folder itself is basically inert. It's explicitly including graphql 4.x-dev in the build matrix that makes this stable module dependent on an unstable module, and I think that's a fairly new thing. But interdependent PRs, infrequent as they may be, are just unavoidable in our setup as far as I can tell.