Mostly around newlines and line continuation.
* percent arrays need special backslash handling in the ast
* Fix offset issue for heredocs with many line continuations (used wrong variable as index access)
* More refined rules on when to simplify string tokens
* Handle line continuations in squiggly heredocs
* Correctly dedent squiggly heredocs with interpolation
* Consider `':foo:` and `%s[foo]` to not be interpolation

https://github.com/ruby/prism/commit/4edfe9d981