Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

Utilize the test generation tool to increase coverage of destructuring
assignment semantics. Previously, only destructuring assignment in the
AssignmentExpression position was tested. With this change applied, the
same tests will assert expected behavior for destructuring assignment in
`for..of` statements, as well.

A limited number of tests are applied to the `for..in` statement as
well, but due to the iteration protocol observed by that statement, many
destructuring tests are not relevant, and others cannot be automatically
generated from this format.

The files in this patch are organized according to the following naming
scheme:

Prefix             | Grammar production
-------------------|-------------------
`array-empty-`     | ArrayAssignmentPattern : [ ]
`array-elision-`   | ArrayAssignmentPattern : [ Elision ]
`array-rest-`      | ArrayAssignmentPattern : [ Elisionopt AssignmentRestElement ]
`array-elem-`      | ArrayAssignmentPattern : [ AssignmentElementList ]
`array-elem-trlg-` | ArrayAssignmentPattern : [ AssignmentElementList , Elisionopt AssignmentRestElementopt ]

Suffix             | Intent
-------------------|-------
`-abpt-close-err`  | The assignment evaluation returns an abrupt completion, and the iterator's `return` method throws an error
`-abpt-close-skip` | The assignment evaluation returns an abrupt completion, but IteratorClose is not invoked
`-abpt-close`      | The assignment evaluation returns an abrupt completion, and IteratorClose is invoked as specified
`-get-err`         | Abrupt completion returned from GetIterator
`-nrml-close-err`  | The assignment evaluation completes, and the iterator's `return` method throws an error
`-nrml-close-null` | The assignment evaluation completes, and the iterator's `return` method returns a non-Object value (there is no corresponding `-abpt-` suffix because the algorithm does not reference the return value in those cases)
`-nrml-close-skip` | The assignment evaluation completes, but IteratorClose is not invoked
`-nrml-close`      | The assignment evaluation completes, and IteratorClose is invoked as specified

Not all suffixes are appropriate for all productions. Suffixes have been
simplified in cases where less specificity is necessary to disambiguate
test cases.