initial nix language support

[fidgetingbits]

EDIT: I removed the original PR text, as no longer relevant and will have made it harder to review.

This PR adds nix language support.

Checklist

• Recorded tests for the new language
• Used "change" / "clear" instead of "take" for selection tests to make recorded tests easier to read
• Added a few specific tests that use "chuck" instead of "change" to test removal behaviour when it's interesting, especially:
  • "chuck arg" with single argument in list
  • "chuck arg" with multiple arguments in list
  • "chuck item" with single argument in list
  • "chuck item" with multiple arguments in list
• Added @textFragment captures. Usually you want to put these on comment and string nodes. This enables "take round" to work within comments and strings.
• Added a test for "change round" inside a string, eg "hello (there)"
• [-] Supported "type" both for type annotations (eg foo: string) and declarations (eg interface Foo {}) (and added tests for this behaviour 😊)
• Supported "item" both for map pairs and list entries (with tests of course)

Supported	Tested	Term	Capture	Definition	Comment
✓	✓	list	@list	List type equivalent	-
✓	✓	inside list	@list.interior	Inside of a list	-
✓	✓	map	@map	Dictionary type equivalent	-
✓	✓	inside map	@map.interior	Inside of a dictionary	-
✓	✓	key	@collectionKey	Dictionary key equivalent	-
✓	✓	funk	@namedFunction	A named function declaration	-
✓	✓	inside funk	@namedFunction.interior	The inside of a lambda declaration	-
✓	✓	funk name	@functionName	Name of declared function	-
✓	✓	lambda	@anonymousFunction	A lambda declaration	-
✓	✓	inside lambda	@anonymousFunction.interior	The inside of a lambda declaration	-
✓	✓	name	@name	Variable name	-
✓	✓	value	@value	Right-hand-side value of an assignment	-
_	_	value	@value	Value returned from a function	-
✓	✓	value	@value	Value of a key-value pair	-
✓	✓	state	@statement	Any single coded statement	-
✓	✓	if state	@ifStatement	An if conditional block	-
✓	✓	condition	@condition	Condition of an if block	-
_	_	condition	@condition	Condition of a while loop	-
_	_	condition	@condition	Condition of a do while style loop	-
_	_	condition	@condition	Condition of a for loop	-
_	_	condition	@condition	Condition of a ternary expression	-
✓	✓	branch	@branch	The resulting code associated with a conditional expression	-
✓	✓	inside branch	@branch.interior	The statements associated with the body of a conditional expression	-
✓	✓	comment	@comment	Single line code comment	-
✓	✓	comment	@comment	Multi-line code comment	-
✓	✓	string	@string	Single line strings	-
✓	✓	string	@string	Multi-line strings	-
✓	✓	-	@textFragment	Used to capture string-type nodes (strings and comments)	-
✓	✓	call	@functionCall	A function call (not a function definition)	-
✓	✓	callee	@functionCallee	Name of the function being called	-
✓	✓	arg	@argumentOrParameter	Arguments to function definition	-
✓	✓	arg	@argumentOrParameter	Arguments to function calls	-
✓	✓	arg	@argumentOrParameter	Interpolated variables in strings	-
_	_	class	@class	Class or structure declaration	-
_	_	inside class	@class.interior	The inside of a class declaration	-
_	_	class name	@className	Name of class or structure declaration	-
_	_	type	@type	Type declarations	-

Checklist

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