Extended Unicode Support

[alistairjevans]

Currently AutoStep will work with the UTF-16 Unicode Range, but we need to support the full unicode range. The scope of this is to have support for (as an example):

Using extended characters, like emojis, as part of the matching text.

Given I have a 🤴 face

Using those characters as arguments.

Given I have a '🎉 🐱‍🐉' argument

See https://github.com/antlr/antlr4/blob/master/doc/unicode.md for antlr details.