Modify the regular expression for native functions' toString value to
satisfy all test cases. Correct the test file's reference to the harness
file. Re-format the test file's assertions to aid debugging in the event
of failure.

This changeset includes tests for early errors and those generated
dynamically by eval. It also accounts for relevant AnnexB extensions.

The millisecond representation of a given Date instance is dependent on
the local system's time zone settings. In order to pass consistently
across contexts, tests for this value must take the system configuration
into account.

Introduce a test harness utility function to encapsulate these concerns.
Re-use this function across all test files that assert the exact
millisecond representation of Date instances.

Closes gh-540

Because the specific value of each constant is specified as a
host-defined approximation, only the value type may be enforced by
Test262.

Except for a small set of expected input/output pairs, both ES5 and
ES2015 define the expected return value of these methods in terms of an
"implementation-dependent approximation." This makes it inappropriate to
enforce expectations for specific values, even if expressed imprecisely.

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.

The project's CONTRIBUTING.md was written with test authors in mind. It
contains details on non-technical metadata (e.g. "author" and "es6id"),
helper function usage, and preferred code structure. In addition, it
elides certain low-level technical details on the requirements for the
runtime environment.

Introduce a new document targeted towards those executing the tests.
Formalize all expectations regarding how the runtime environment should
be defined, how metadata should be interpreted, and how results should
be understood. This information has overlap with the CONTRIBUTING.md
file, but it also contains details that are irrelevant to test authors.

This document can serve as a more formal contract between Test262 and
the implementors who consume it. This allows Test262 to unambiguously
document future modifications to the formal requirements which in turn
supports consumers who maintain their own test harnesses.

Some tests for `eval` assert the equality of key enumeration on the
global object, comparing the ordering when the object is referenced
through eval.

Based on the test bodies and the "info" field in their metadata, these
tests appear to have been written under the mistaken impression that
erroneous creation of an environment record would be observable through
the `this` value.

In reality, the value in such cases resolves to the global object. That
renders these tests redundant and overly complex--none of the
distinctions between each test actually demonstrates a different
behavior.

Remove the redundant tests and introduce three new tests asserting the
correct resolution of the `this` keyword for direct eval code from
within the global scope and from within function scope.

Introduce test generation tool

See the proposal at
https://tc39.github.io/Function-prototype-toString-revision/

Because Test262 asserts the strict equality of
`Array.prototype.toString` and `TypedArray.prototype.toString`, tests
for properties of the object do not need to be reproduced in both
location.

Ref gh-526

https://github.com/tc39/proposal-string-pad-start-end/issues/23

Closes gh-564

Ref: https://github.com/tc39/test262/pull/536#issuecomment-200455389

Correct example in contribution guidelines

Test specific behaviour for Integer Indexed exotic objects, WRT the
following internal methods:

- [[GetOwnProperty]]
- [[HasProperty]]
- [[DefineOwnProperty]]
- [[Get]]
- [[Set]]
- [[OwnPropertyKeys]]

Avoid false positives

As written, the example for asserting runtime errors is written with an
early error. Because the error is expected to be reported prior to
program execution, the `assert.throws` function cannot be used to detect
it.

Demonstrate the usage of the helper function with a runtime error.

Add syntax tests for declaration restrictions

Add tests for Number.{MAX,MIN}_SAFE_INTEGER

Add tests for `debugger` statement

As written, the test for `Math.random` would pass if the runtime
erroneously produced a non-numeric value. Add the necessary assertions
to guard against this case.

Improve coverage %ThrowTypeError% and default class constructors

Make asynchronous test configuration explicit