Bugfix: Refine support for LAEA grids via NetCDF and GRIB2 files

[JohnHalleyGotway]

Describe the Problem

Development for #1693 ADDED support for reading LAEA grids from GRIB2 files. However, it also REMOVED the existing support for reading LAEA grids from CF-compliant NetCDF files. As such, we commented out the existing unit test that tested that functionality (see <test name="plot_data_plane_LAEA_NCCF"> in unit_plot_data_plane.xml).

This task is to restore that support for reading LAEA data from CF-compliant NetCDF files. Recommend paying careful attention to Lambert azimuthal equal area documentation. And please remember to uncomment the plot_data_plane_LAEA_NCCF unit test mentioned above.

Only need to fix this for the develop branch prior to the MET-11.1.0 release.

Expected Behavior

Support LAEA grids read from both GRIB2 and CF-complaint NetCDF files.

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[JohnHalleyGotway]

@mpm-meto and @robdarvell, @rgbullock is working on this issue. He is using a MetOffice data file for testing that is centered on the United Kingdom.
20230302T2100Z-visibility_at_screen_level.nc

I am wondering if you perhaps have a sample data file that's further away from the prime meridian with which he could also test? For example, in the past you send us data centered over India. Can you provide a sample LAEA CF-Compliant NetCDF file that covers the India domain?

[mpm-meto]

I can ask. Perhaps UM partners now running IMPROVER will have some sample data but we don't have any LAEA data over other parts of the world.

[JohnHalleyGotway]

OK, thanks for checking. We'll do the best we can with UK LAEA NetCDF sample data we have. If you do get your hands on NetCDF data for additional LAEA domains, please pass it along.

[JohnHalleyGotway]

Note that I renamed this issue to clarify that 2 changes are needed:

1. Restore support for parsing LAEA grids from CF-compliant NetCDF files.
2. Refine support for parsing LAEA grids from GRIB2 files.

For the latter, the MET-11.1.0-rc1 version does not properly parse longitudes from the LAEA GRIB2 metadata. The problem lies in the GRIB2C library which MET uses to retrieve that metadata. In the sample GRIB2 files over the United Kingdom, the 2 longitudes defining the LAEA grid have negative values. The GRIB2C library does not properly parse that negative value.

Both 1. and 2. are now fixed. For 2., MET now reprocesses the 4 bytes which constitute the value and reprocess them looking for a negative.