Fixed issue #15852 - adding spaces between simple selectors where no spaces should be.
Fixed issue where trailing comma was being removed from item list in array literal.
Fixed issue where trailing comma in object literal list was causing error to be thrown incorrectly.
Added a common ContextError object to the CSS and JS parser event arguments to simplify error handling.
Refactored AST nodes to only have one class with yield statements, thereby reducing executable size.