close #16593: setting ecolor turns off color cycling

[story645]

Co-authored-by: @tacaswell

PR Summary

Removed ecolor is not none from the codepath choosing between cycler and no cyclers; ecolor is none still defaults to cycler. This is arguably the preferred behavior as the user specifying the color of the errorbars does not tell us anything about what colors they'd like the actual plots to be (which is what cycler prefers).
A longer discussion should probably be had about cycler semantics - in which cases should the code default to the color the user passed in - I'm team basically any artist color not explicitly set should be controlled by the cycler.

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant

[WeatherGod]

Looks like there are some style issues in the new test:

./lib/matplotlib/tests/test_axes.py:3269:1: E302 expected 2 blank lines, found 1
./lib/matplotlib/tests/test_axes.py:3275:17: W291 trailing whitespace
./lib/matplotlib/tests/test_axes.py:3276:10: E111 indentation is not a multiple of four
./lib/matplotlib/tests/test_axes.py:3276:10: E117 over-indented
./lib/matplotlib/tests/test_axes.py:3276:35: E251 unexpected spaces around keyword / parameter equals
./lib/matplotlib/tests/test_axes.py:3276:43: E203 whitespace before ','
./lib/matplotlib/tests/test_axes.py:3276:60: W291 trailing whitespace
./lib/matplotlib/tests/test_axes.py:3278:1: W293 blank line contains whitespace
./lib/matplotlib/tests/test_axes.py:3281:10: E111 indentation is not a multiple of four
./lib/matplotlib/tests/test_axes.py:3281:10: E117 over-indented
./lib/matplotlib/tests/test_axes.py:3281:35: E251 unexpected spaces around keyword / parameter equals
./lib/matplotlib/tests/test_axes.py:3281:59: W291 trailing whitespace
./lib/matplotlib/tests/test_axes.py:3283:1: W293 blank line contains whitespace
./lib/matplotlib/tests/test_axes.py:3284:1: E302 expected 2 blank lines, found 1

[tacaswell]

This probably needs an API change note as something that did not used to cycle is now cycling?

[story645]

@tacaswell not in love w/ the language I put there, but added behavior change entry.
@WeatherGod thanks, totally forgot to check on flake issues!

[tacaswell]

modulo fixing the doc builds (think the decoration is too short)