Update the STASH_TRANS table

[trexfeathers]

✨ Feature Request

Include the latest STASH codes in the STASH_TRANS dictionary:

iris/lib/iris/fileformats/_ff_cross_references.py

Lines 13 to 20 in 6fbf619

	Stash = namedtuple('Stash', 'grid_code field_code pseudo_level_type')
	STASH_TRANS = {
	"m01s00i001": Stash(1, 8, 0),
	"m01s00i002": Stash(18, 56, 0),
	"m01s00i003": Stash(19, 57, 0),
	"m01s00i004": Stash(1, 19, 0),

For backwards compatibility it is important that we limit to ADDITIONS and UPDATES, no deletions. Some codes have likely been retired since the last update; we can just leave those as they are.

Motivation

Iris depends on the contents of STASH_TRANS for various functions. The dictionary has not been updated for several years, and I have encountered examples where absence of a STASH code causes faulty file loading - e.g. not knowing that a phenomenon is associated with cell edges, thus producing coordinates with the wrong number of points (thanks to @ukmo-juan-castillo for the example).

Additional context

We historically could rely on parsing Metarelate to give what we needed (e.g. #973 (comment)). But now that Metarelate has been retired, it would still be possible to automatically parse the contents from other sources.

Met Office Codes Registry : um/stash offers many download formats, but does not appear to be up to date (2019 when I checked).

Those of us at the UK Met Office do have access to the latest 'STASHmaster' file, although I won't share details of the directory structure publicly.