Add Jansi auto detection.

[charphi]

See #483

[remkop]

Looks good!
Do you think you can add a unit test for this?

[codecov-io]

Codecov Report

Merging #486 into master will decrease coverage by 0.06%.
The diff coverage is 33.33%.

@@             Coverage Diff              @@
##             master     #486      +/-   ##
============================================
- Coverage     89.15%   89.09%   -0.07%     
  Complexity      281      281              
============================================
  Files             4        4              
  Lines          3846     3851       +5     
  Branches        931      932       +1     
============================================
+ Hits           3429     3431       +2     
- Misses          207      209       +2     
- Partials        210      211       +1

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/picocli/CommandLine.java	89.06% <33.33%> (-0.08%)	153 <0> (ø)
src/main/java/picocli/AutoComplete.java	86.55% <0%> (ø)	80% <0%> (ø)	⬇️

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[charphi]

I've added a test but it doesn't increase the code coverage.
I don't know how to properly test this since it depends on runtime context.

[remkop]

@charphi Sorry for my late response. Thanks for adding a test! I'll try to take a closer look later today.