Added more destructuring tests

Added:
* Destructuring parameters
* Destructuring defaults
* Destructuring with rest
* Update to the basic test to check for nested structures, aliasing,
and skipping array elements.

Also, unrelatedly added:
* Symbol.for() and Symbol.keyFor() test
* Array#[Symbol.unscopables] test
* Corrections to a few test results.

Thanks to @rwaldron for feedback.