Replace width/height in future AreaDefinition with "shape" argument

[djhoese]

This was discussed in a previous PR regarding cleaning up AreaDefinitions. The basic idea is to reduce the number of arguments passed to an AreaDefinition to keep the interface a little cleaner and simpler. This PR does this by grouping the width and height arguments into a single "shape" tuple.

This also makes it easier to create AreaDefinitions with more than 2 dimensions in the long long term.

• Closes #xxxx
• Tests added
• Tests passed
• Passes git diff origin/main **/*py | flake8 --diff
• Fully documented

[codecov]

Codecov Report

Merging #533 (3cb9861) into main (82b9373) will increase coverage by 0.00%.
Report is 7 commits behind head on main.
The diff coverage is 91.66%.

@@           Coverage Diff           @@
##             main     #533   +/-   ##
=======================================
  Coverage   94.25%   94.26%           
=======================================
  Files          82       82           
  Lines       13030    13059   +29     
=======================================
+ Hits        12282    12310   +28     
- Misses        748      749    +1     

Flag	Coverage Δ
unittests	94.26% <91.66%> (+<0.01%)	⬆️

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

Files Changed	Coverage Δ
pyresample/test/test_resamplers/test_nearest.py	100.00% <ø> (ø)
pyresample/utils/rasterio.py	62.50% <50.00%> (ø)
pyresample/area_config.py	90.58% <100.00%> (ø)
pyresample/future/geometry/area.py	100.00% <100.00%> (ø)
pyresample/test/conftest.py	98.47% <100.00%> (+0.01%)	⬆️
pyresample/test/test_geometry/test_area.py	99.22% <100.00%> (+<0.01%)	⬆️

... and 3 files with indirect coverage changes

[coveralls]

coverage: 93.84% (-0.02%) from 93.864% when pulling 3cb9861 on djhoese:feature-areadef-shape into 82b9373 on pytroll:main.

[mraspaud]

LGTM, just one small improvement idea