Read only, informational only.
Name of the ansi include file used supports_ansi.dart is the default,
or the dart.libary.io version supports_ansi_io.dart
or the dart.library.html version supports_ansi_web.dart.
Read only. Chalk does not use it's value although in some
situation a user might use this to set the Chalk ansi color level
(or something) I have left it here only for completeness.
Within the common debug consoles this variable is essentially
worthless because they return FALSE from both VSCode debug console
and IntelliJ/Android Studio debug consoles.
(This is because dart just checks for 'xterm' string being present in
the 'TERM' environmental variable of the console..)
See https://github.com/dart-lang/sdk/issues/31606 and
https://github.com/dart-lang/sdk/issues/41770 for more info.