Reinstate grib as_messages.

[pp-mo]

This function was removed by #1941, when it should just have been deprecated.
The test iris.tests.unit.fileformats.grib test "test_as_messages" is not reinstated, as "test_as_pairs" covers it.
As a complete aside, I also spotted the ECMWF link in the module header was broken + fixed that.

[pp-mo]

Given this, I think we again have a consistent form of grib support.
This can serve as a sensible basis for subbing out grib support to "iris_grib" as proposed here

Remaining PR not included :
#1755 "grib1 future" is not in included in this.
It seeks to provides Grib1 support through the new "strict" loader , but we aren't finished agreeing it.
It should be pretty easy to carry those changes over into the new iris-grib package when required.
The point is, hopefully, that by pushing those problems into iris-grib, we don't need to provide alternatives to grib1 loading before cutting Iris 1.10.
Instead we propose:

• iris 1.10 deprecates iris.fileformats.grib in favour of iris-grib
• iris 2.0 removes iris.fileformats.grib
• grib-api 1.0 retains both 'old' + 'new' grib loaders
• non-strict support can be removed at grib-api 2.0

[pp-mo]

Remaining PR not included :

There are also a couple of older ones still in the pot, but I think no urgency on these ? ...

• Implement fault tolerant GRIB2/PP loading. #1703 @ajdawson "fault tolerant Grib loading."
• Add GRIB2 load support for GDT-50 (spherical harmonics). #1687 "Add GRIB2 load support for GDT-50 (spherical harmonics)."

[rhattersley]

This can serve as a sensible basis for subbing out grib support to "iris_grib" as proposed here

NB. Irrespective of whether we go the iris-grib route we want this change.

[rhattersley]

The test iris.tests.unit.fileformats.grib test "test_as_messages" is not reinstated

I don't understand why you've not reinstated this - by default I'd rather it was back again.

[rhattersley]

With the exception of the test_as_messages question I'm 👍

[pp-mo]

I don't understand why you've not reinstated this

Ok, you're right.

[rhattersley]

Super, thanks. 👍 Any chance of a squash?

[pp-mo]

sqwished !

[rhattersley]

Excellent - that gets grib handling back into the state where it doesn't need a major version change. 👍