* unpaired surrogate escape sequences

This is based on André Bargull's test case in
<https://bugzilla.mozilla.org/show_bug.cgi?id=1464757>.

Related to https://github.com/tc39/ecma262/pull/1177

This reverts commit a01de4a7.

* additional BigInt JSON tests

* single quotes

* BigInt stringify order of steps

* Add tests for abrupt completions during JSON.parse

Due to the use of the IsArray abstract operation, observing many of the
targeted semantics requires the use of a Proxy exotic object. Mark the
tests that require this unrelated ES2015 feature using a dedicated
"features" flag.

* Express JSON syntax tests with multiple assertions

When written with a single assertion, this test verifies only that "one
or more" of the Unicode points produces a SyntaxError. Re-factor the
test so that parsing behavior for each code point can be tested in
isolation.

* Re-introduce assertion

ECMAScript edition 2016 relies on the Unicode standard at version 8.0.0.
As part of a larger effort to update Test262 accordingly, the assertion
for the SyntaxError resulting from the use of the Mongolian Vowel
Separator (U+180E) was removed. However, ECMA-401 (The JSON Data
Interchange Format) continues to describe "insignificant whitespace" as
follows:

> Insignificant  whitespace  is  allowed  before  or  after  any  token.
> The  whitespace  characters  are:  character  tabulation  (U+0009),
> line  feed  (U+000A),  carriage  return (U+000D),  and  space
> (U+0020)

And because ECMA262 specifies step 2 of the `JSON.parse` algorithm as
follows:

> 2. Parse JText interpreted as UTF-16 encoded Unicode points (6.1.4) as
>    a JSON text as specified in ECMA-404. Throw a SyntaxError exception
>    if JText is not a valid JSON text as defined in that specification.

...the use of U+180E between JSON tokens should continue to produce a
SyntaxError, regardless of ECMA262's updated Unicode standard.

* fixup! Express JSON syntax tests with multiple assertions

Ref. https://hashseed.blogspot.com/2014/08/in-ecma-262-5.html
Ref. https://github.com/tc39/ecma262/pull/300#issuecomment-181376767
Ref. https://github.com/mathiasbynens/regexpu-core/commit/9b10d2a597d4e56b236cae0f9aa2f21a9c6d1122

Fix and add @anba’s U+180E tests

Note: Already uses the updated DataView function lengths from tc39/ecma262#266 (ES2016 Draft 2015-12-20)

This function is equivalent to `$ERROR` (which is automatically included
in test environments). Remove the harness file that defines the
function, remove references to the file from test `includes` lists, and
update scripts to instead invoke the `$ERROR` function.