Correctly (re)order dimensions for bfmi and plot_energy

[sethaxen]

Description

This PR ensures that bfmi and plot_energy compute the same thing if the named dimensions (chain, draw) are instead ordered as (draw, chain) and adds a test.

Addresses part of #2102 (comment)

Checklist

• Does the PR follow official
  PR format?
• Does the PR include new or updated tests to prevent issue recurrence (using pytest fixture pattern)?
• Is the code style correct (follows pylint and black guidelines)?
• Is the fix listed in the Maintenance and fixes
  section of the changelog?

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📚 Documentation preview 📚: https://arviz--2126.org.readthedocs.build/en/2126/

[codecov]

Codecov Report

Merging #2126 (45764ca) into main (3c2dc6e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2126   +/-   ##
=======================================
  Coverage   90.76%   90.77%           
=======================================
  Files         117      117           
  Lines       12501    12501           
=======================================
+ Hits        11347    11348    +1     
+ Misses       1154     1153    -1     

Impacted Files	Coverage Δ
arviz/plots/energyplot.py	88.88% <100.00%> (+5.55%)	⬆️
arviz/stats/diagnostics.py	98.96% <100.00%> (ø)

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