* Eliminate well-known symbols in the checker: 2021 edition
* Actually update the lib text to say unique symbol, too (this is unneeded with compat code in place, but this makes goto-def make more sense)
* Add test showing mismatched symbol constructor type interop
* Add more test cases for some other related issues this fixes
* Revert computed name change
* Style comments
* Improve typing for Generators and Async Generators
* Add TReturn and TNext to Iterator, IterableIterator, etc.
* Update ts internal Iterator to be assignable from global Iterator
* Make 'done' optional in IteratorYieldResult
* Revert Iterable and IterableIterator to simpler versions plus other fixes
* Add additional inference tests
* Added additional tests
* PR cleanup and minor async iteration type fix
* Updated diagnostics message and added non-strict tests
* Fix expected arity of Iterator/AsyncIterator
Wesley Wigham
Ron Buckton
Kagami Sascha Rosylight