* Add Function.prototype.toString tests for many function forms
* Add non-const computed property name to Function.prototype.toString tests
* Split class method tests into class-expression and class-statement tests
* Add tests for unnamed function expression forms
* Add tests for async (generator) methods in class contexts
* Add test case for Function.prototype.toString on async arrow function

After @rwaldron's feedback:

The purpose of the `!` operator is to evaluate an UnaryExpression,
coerce the result to a boolean value and then return the negated
value of that operation. But that's not what you're trying to do at
all—you just want to evaluate the expression to the right of the
operator, nothing more, nothing less. In this specific case, you
don't even really care about the evaluation, the goal is write
valid (or invalid, as the case may be) syntax that is will be
parsed according to a specific grammar rule that requires some
operator to signal that the thing is an expression and not a Block
Statement.

Tests doesn't use async functionality and don't call $DONE, so remove
"async" flag:
- src/params/error/async-gen-named-func-expr.template
- test/language/expressions/async-generator/params-named-dflt-abrupt.js
- test/language/expressions/async-generator/params-named-dflt-ref-later.js
- test/language/expressions/async-generator/params-named-dflt-ref-self.js

Intl.PluralRules.prototype is no longer a Intl.Prototype instance:
- test/intl402/PluralRules/prototype/prototype.js

Intl.PluralRules throws an error when called as a function:
- test/intl402/PluralRules/undefined-newtarget-throws.js

Module namespace objects call OrdinaryDelete for symbol properties:
- test/language/module-code/namespace/internals/delete-non-exported.js

Async generators no longer retrieves "done" property twice:
- src/async-generators/yield-star-async-next.case
- src/async-generators/yield-star-async-return.case
- src/async-generators/yield-star-async-throw.case

Minor units of CLF is 4, so we need to test with maximumFractionDigits=3
to get an error:
- test/intl402/NumberFormat/dft-currency-mnfd-range-check-mxfd.js

DateTimeFormat.prototype.formatToParts length property was changed from
0 to 1:
- test/intl402/DateTimeFormat/prototype/formatToParts/length.js

minimumSignificantDigits and maximumSignificantDigits properties are
only retrieved once:
- test/intl402/NumberFormat/11.1.1_32.js

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

Bug was reported by @anba at
https://github.com/tc39/ecma262/pull/852#issuecomment-291781031

Without this change, you'd expect a RangeError rather than a TypeError.

Add escape-above-astral.js to cover escaping code units as encoded from extended unicode escape. (#942)

In https://github.com/tc39/ecma262/pull/853 , standard semantics
for this case are proposed. This patch tests the case.

The change is proposed in https://github.com/tc39/ecma262/pull/856
as a fix to https://github.com/tc39/ecma262/issues/855

Here, the ToNumber coercion is done only once, rather than on each
iteration. It does not appear that there were previously any
tests against repeated coercion for this parameter previously.

Tested this test against V8, which failed, as V8 implements the
current spec rather than the proposed one.

Closes #888

These tests are regression tests for V8 failures at top of tree,
https://bugs.chromium.org/p/v8/issues/detail?id=6015
https://bugs.chromium.org/p/v8/issues/detail?id=6016

Neither issue is present in JSC or SpiderMonkey. They are fixed
by the V8 patch
https://codereview.chromium.org/2717613005

This test comes from a note in the specification under toFixed.
It fails in ChakraCore and passes in other engines that I tested.

This test is only valid with the PR in https://github.com/tc39/ecma262/pull/852