Make arguments to engine optional

[AndreasArvidsson]

Checklist

• [/] I have added tests
• [/] I have updated the docs and cheatsheet
• [/] I have not broken the cheatsheet

[pokey]

update from meet-up re null tree-sitter:

• [x] if tree-sitter is null, create DisabledLanguageDefinitions that just doesn't support any languages
• [x] remove tree-sitter debug prints
• [x] allow null to pass to parse tree action for now and just have null check there that throws

goal for all this stuff is to allow undefined components to pass into engine, and contain all resulting null checks to createEngine, and create a DisabledFoo in response. Note that third checkbox above fails this criterion, but we don't need to be dogmatic

[AndreasArvidsson]

ready!

[AndreasArvidsson]

Ok this pull request has now been stripped off the Tree sitter stuff