Since there are only a number of statements where labels can actually be
used we now also only store labels when necessary.
Also now tracks the first continue usage of a label since this might not
be valid but that can only be determined after we have parsed the
statement.
Also ensures the correct error does not get wiped by load_state.
Since we have the to_reference method on every expression class we must
somehow communicate it did not actually return a reference.
This (ab)uses the fact that property name is only invalid with the
default constructor and already has is_valid().
The ECMAScript spec says that Date parsing can support any number of
implementation-defined date formats. So let's support a format commonly
used on the web. And let Core::DateTime do the heavy lifting. :^)
At a later point this will indicate whether some FunctionObject "has a
[[Construct]] internal method" (separate from the current FunctionObject
call() / construct()), to help with a more spec-compliant implementation
of [[Call]] and [[Construct]].
This means that it is no longer relevant to just NativeFunction.
Also add the internal slot names as comments, and separate them into
groups of spec and non-spec members.
This will make it easier to compare the implementation code with the
spec, as well as identify internal slots currently missing or only
present on FunctionObject.
The old name is the result of the perhaps somewhat confusingly named
abstract operation OrdinaryFunctionCreate(), which creates an "ordinary
object" (https://tc39.es/ecma262/#ordinary-object) in contrast to an
"exotic object" (https://tc39.es/ecma262/#exotic-object).
However, the term "Ordinary Function" is not used anywhere in the spec,
instead the created object is referred to as an "ECMAScript Function
Object" (https://tc39.es/ecma262/#sec-ecmascript-function-objects), so
let's call it that.
The "ordinary" vs. "exotic" distinction is important because there are
also "Built-in Function Objects", which can be either implemented as
ordinary ECMAScript function objects, or as exotic objects (our
NativeFunction).
More work needs to be done to move a lot of infrastructure to
ECMAScriptFunctionObject in order to make FunctionObject nothing more
than an interface for objects that implement [[Call]] and optionally
[[Construct]].
