(Towards #2381 #2674) add min max access types and new LFRic builtins

[arporter]

This is a step towards both #2381 (generalising global reductions) and #2674 (new field_min_max builtin). It attempts to reduce the size of #3222 by only adding the two new access types for reductions as well as the skeletons for the new builtins.