Fixed IndexedData to properly handle world coordinates

[astrofrog]

@Cadair - this will allow world coordinates to be shown when using the pixel selection tool in glue-solar!

Fixes #1961

[codecov]

Codecov Report

Merging #2081 into master will increase coverage by <.01%.
The diff coverage is 88.63%.

@@            Coverage Diff             @@
##           master    #2081      +/-   ##
==========================================
+ Coverage   87.98%   87.98%   +<.01%     
==========================================
  Files         245      245              
  Lines       22101    22131      +30     
==========================================
+ Hits        19445    19472      +27     
- Misses       2656     2659       +3

Impacted Files	Coverage Δ
glue/core/coordinates.py	90.62% <100%> (-0.42%)	⬇️
glue/core/data_factories/pandas.py	85% <100%> (ø)	⬆️
glue/core/data_derived.py	97.58% <100%> (+1.18%)	⬆️
glue/core/data.py	92.05% <79.16%> (-0.31%)	⬇️

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