Extend Resolve support for AncillaryVariable and CellMeasure

[bjlittle]

⚙ Feature Request

To extend the capability of iris.common.resolve.Resolve to be able to handle and resolve iris.coords.AncillaryVariable and iris.coords.CellMeasure metadata.

Motivation

This will enhance cube arithmetic to include this metadata in its resultant iris.cube.Cube result. Also it will provide a more complete and richer, generic way to combine common metadata through the direct use of iris.common.resolve.Resolve.