The special empty value (that we use for array holes, Optional<Value>
when empty and a few other other placeholder/sentinel tasks) still
exists, but you now create one via JS::js_special_empty_value() and
check for it with Value::is_special_empty_value().
The main idea here is to make it very unlikely to accidentally create an
unexpected special empty value.
This changes the remaining uses of the following functions across LibJS:
- String::format() => String::formatted()
- dbg() => dbgln()
- printf() => out(), outln()
- fprintf() => warnln()
I also removed the relevant 'LogStream& operator<<' overloads as they're
not needed anymore.
This patch teaches UpdateExpression how to use a Reference. Some other
changes were necessary to keep tests working:
A Reference can now also refer to a local or global variable. This is
not fully aligned with the spec since we don't have a Record concept.
Expression nodes can now be asked to produce a Reference. We then use
this to implement the "delete" operator without downcasting the child
node to a MemberExpression manually.
