Add CORDEX domain target grids for regridding

[ghossh]

Description

Adds support for using standard CORDEX domain names, such as EUR-11, as target_grid values in the regrid preprocessor.

Previously, target_grid: EUR-11 was treated as an MxN grid specification and failed with:

ValueError: Invalid MxN cell specification for grid, got 'EUR-11'.

Close #3088

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[codecov]

Codecov Report

❌ Patch coverage is 46.15385% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.01%. Comparing base (4127673) to head (a96e132).
⚠️ Report is 40 commits behind head on main.

Files with missing lines	Patch %	Lines
esmvalcore/preprocessor/_regrid.py	44.73%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3096      +/-   ##
==========================================
- Coverage   96.14%   96.01%   -0.13%     
==========================================
  Files         267      267              
  Lines       15771    15803      +32     
==========================================
+ Hits        15163    15174      +11     
- Misses        608      629      +21     

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[bouweandela]

Looks like a great start! Could you take a look at the checklist? A few things to do would be

• sign the CLA
• add a unit test
• add documentation

Usually you can find advice on how to go about that in the pull request template, but in case you missed it you can find it here: https://github.com/ESMValGroup/ESMValCore/blob/main/.github/pull_request_template.md

[bouweandela]

Maybe you could simplify this code by using ncdata.iris_xarray.cubes_to_xarray to convert the xarray.Dataset to an iris.cube.Cube directly?