remove and inline the use of package:ansi_up

[devoncarew]

• remove and inline the use of package:ansi_up

This allows us to remove one dep - package:ansi_up. The code for the AnsiParser class is mostly taken from third_party ansi_up/ansi_up.dart, w/ some simplifications and code paths that were never taken removed. It should have the same functionality as the previous code for the parts we were using.

This does not deprecate package:ansi_up, though that would be a good future step.

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