Fix Scene.coarsest/finest_area not returning consistent results

[djhoese]

In rare cases some readers return multiple AreaDefinitions or SwathDefinitions of the same resolution, but with different coordinates. The case I ran into is the AMSR2 sensor with its A and B views. They have the same resolution (shape), but are slightly shifted from one another. Having Scene.coarsest_area and Scene.finest_area return either one of these is fine, but you run into issues if they are not consistent. In my case I was using the result to freeze a DynamicAreaDefinition and then compare my final geotiffs against expected results. Currently the Scene's choice between the A and B geometries is based on the order that the DataArrays is sorted which is essentially random. My tests would sometimes match and sometimes not match depending on what order was ultimately used.

This PR fixes this to include other properties of the geometry objects to decide which one should be returned. It isn't perfect, especially when it comes to SwathDefinitions, but it is a start.

• Closes #xxxx
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

Merging #2098 (3bd2473) into main (20434bf) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2098   +/-   ##
=======================================
  Coverage   93.89%   93.90%           
=======================================
  Files         283      283           
  Lines       42589    42615   +26     
=======================================
+ Hits        39991    40017   +26     
  Misses       2598     2598           

Flag	Coverage Δ
behaviourtests	4.71% <8.19%> (+<0.01%)	⬆️
unittests	94.46% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/readers/viirs_sdr.py	86.94% <100.00%> (ø)
satpy/scene.py	93.12% <100.00%> (+0.14%)	⬆️
satpy/tests/test_scene.py	99.46% <100.00%> (+<0.01%)	⬆️

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[coveralls]

Coverage increased (+0.003%) to 94.401% when pulling 3bd2473 on djhoese:bugfix-minmax-area-amsr2 into 20434bf on pytroll:main.

[mraspaud]

LGTM, thanks for reorganising the tests too!