* Output simple array destructuring assignments to ES2015
* Output simple object destructured assignments to ES2015
* Compile shorthand object properties to ES2015 shorthand properties
This dramatically improves the appearance of destructured imports.
* Compile default values in destructured assignment to ES2015
* Rename `wrapInBraces` to `wrapInParentheses`, and `compilePatternMatch` to `compileDestructuring`, for clarity; style improvements (no `==` or `!=`, etc.)
* Don’t confuse the syntax highlighter
* Comment Assign::compilePatternMatch a bit
* Assignment expressions in conditionals are a bad practice
* Optional check for existence that only checks `!== undefined`, not `!= null`, to follow ES convention that default values only apply when a variable is undefined, not falsy
* Add comments; remove unnecessary array splats in function tests
* The fallback destructuring code should apply default values only if `undefined`, not falsy, to follow ES spec
* Support destructuring in function parameters (first pass); catch destructured reserved words
* Destructured variables in function parameter lists shouldn’t be added to the function body with `var` declarations; treat splat array function parameters the legacy way to avoid rethinking #4005
* Remove redundancy in undefined-only check for existence; fix passing option to check
* Fix undefined redundancy
* Simplify getting the variable name
* Reimplement “check for existence if not undefined” without creating a new operator
* `Obj::isAssignable` should not mutate; pass `lhs` property in from `Assign` or `Code` to child arrays and objects so that those child nodes are set as allowable for destructuring
* Revert changes to tests
* Restore revised test for empty destructuring assignment
