Add iteration and other events related things

[kaleidawave]

• Add basic destructuring into array declaration based on iterator protocol object
• Symbols -> Symbol
• Adds Accumulator, a structure for handling returns state (sort of control flow graph, but not really)
• Adds --basic flag that basically turns off event application (in an attempt to simplify)
• Add loop unrolling inside of event application. This enables Array.prototype.contains narrowing for arrays with known members and length
• Basic TypeScript enum support
• Map.prototype.get and Map.prototype.set constant functionality

TODO

• Destructuring assignment for declarations
• for of
• Generators
• Promises
• Length calculation
• Spreads
• Array.prototype[Symbol.iterator]
• More testing on actual codebases
• More array methods working on unknown
• Array.prototype.filter narrowing and possibly Map?
• Map item checking
• Maybe more RegExp narrowing
• More unknown object stuff (examples in staging.md)

[kaleidawave]

Would love to merge some of the improvements now (for the release) but unfortunately I think a lot more could be done on this. I have tested this a bit on some projects and unfortunately while there are improvements it doesn't quite completely clear some event / control flow issues.

There are a few issues with the parent field handling on SubstitutionArguments but unfortunately the changes caused a bunch of regressions.