Fix broken mesh examples

[ukmo-ccbunney]

Description

Closes: #6972

Fixes the use of iris.ugrid.MeshXY and iris.ugrid.Connectivity in the Mesh Conversion examples.

Also fixes missing AuxCoords in the WAVEWATCH III Mesh example.

Note: Banking this as a draft PR for now as we might want to use the planned "Add cube as component to cube" functionality proposed in #6829.

Checklist

Important

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• Included a What's New entry
• (N/A) Incorporated type hints in any changed code
• Checked if tests need updating
• Checked if benchmarks need updating
• Checked if documentation needs updating
  • Docstrings (we love code examples!)
  • User Manual pages
• Checked if dependencies need updating
• Confirmed that the GitHub 'checks' on this PR are passing ✅
  (further reading)

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.15%. Comparing base (5d7ca14) to head (e753a66).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7168   +/-   ##
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  Coverage   90.15%   90.15%           
=======================================
  Files          91       91           
  Lines       24990    24990           
  Branches     4687     4687           
=======================================
  Hits        22529    22529           
  Misses       1683     1683           
  Partials      778      778           

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[ukmo-daisybrown]

Thank you so much for this @ukmo-ccbunney I was just looking at this exact example and trying to get it to work! You've saved us (me) a lot of effort, but we were curious how you came across this issue with the SMC example in the first place?

[ukmo-ccbunney]

Thank you so much for this @ukmo-ccbunney I was just looking at this exact example and trying to get it to work! You've saved us (me) a lot of effort, but we were curious how you came across this issue with the SMC example in the first place?

I spotted it after someone came to the AVD Surgery with a related issue; I directed them to the example code and it failed. 😬