Improve how we handle reprojection

[astrofrog]

Currently, when reprojecting an image to another image, we are limiting the footprint of the final image to the original one we are reprojecting to, but this isn't right - we should reproject to all available pixels in the image viewer axes.

Remaining to-dos:

• Add back some kind of caching infrastructure, but in get_fixed_resolution_buffer since it is an optimization that would be useful for all callers.
• Fix tests marked as xfail
• Release new version of mpl-scatter-density and up minimum requirement
• Make Python export work for reprojection
• Deal with aggregation
• Test out with 3D viewers to see if it will be appropriate
• Make array maker be callable rather than have a get_array method
• Check Python export with transposed data

Address in future pull requests:

• See if the base get_fixed_resolution_buffer method can be optimized, or needs optimizing

[codecov]

Codecov Report

Merging #1895 into master will increase coverage by 0.04%.
The diff coverage is 96.52%.

@@            Coverage Diff             @@
##           master    #1895      +/-   ##
==========================================
+ Coverage   85.58%   85.63%   +0.04%     
==========================================
  Files         236      238       +2     
  Lines       21066    21227     +161     
==========================================
+ Hits        18030    18177     +147     
- Misses       3036     3050      +14

Impacted Files	Coverage Δ
glue/_deps.py	63.8% <ø> (ø)	⬆️
glue/viewers/image/composite_array.py	93.54% <100%> (-1.25%)	⬇️
glue/core/component.py	96.02% <100%> (+0.59%)	⬆️
glue/core/data.py	89.26% <100%> (+0.06%)	⬆️
glue/viewers/image/python_export.py	91.42% <100%> (+3.92%)	⬆️
glue/core/component_link.py	85.34% <100%> (ø)	⬆️
glue/viewers/image/viewer.py	89.86% <100%> (ø)	⬆️
glue/viewers/image/layer_artist.py	90.69% <100%> (-3.62%)	⬇️
glue/viewers/scatter/python_export.py	97.16% <100%> (+0.02%)	⬆️
glue/core/fixed_resolution_buffer.py	95.09% <95.09%> (ø)
... and 9 more

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