operator= for JS::SafeFunction was missing the CallableKind parameter
in the call to init_with_callable. This was not picked up before as
nothing used operator= on JS::SafeFunction.
Template argument are checked to ensure that the `Out` type is equal or
convertible to the type returned by the invokee.
Compilation now fails on:
`Function<void()> f = []() -> int { return 0; };`
But this is allowed:
`Function<ErrorOr<int>()> f = []() -> int { return 0; };`
Note that this still keeps the old behaviour of putting things in std by
default on serenity so the tools can be happy, but if USING_AK_GLOBALLY
is unset, AK behaves like a good citizen and doesn't try to put things
in the ::std namespace.
std::nothrow_t and its friends get to stay because I'm being told that
compilers assume things about them and I can't yeet them into a
different namespace...for now.
SafeFunction automatically registers its closure memory area in a place
where the JS garbage collector can find it.
This means that you can capture JS::Value and arbitrary pointers into
the GC heap in closures, as long as you're using a SafeFunction, and the
GC will not zap those values!
There's probably some performance impact from this, and there's a lot of
things that could be nicer/smarter about it, but let's build something
that ensures safety first, and we can worry about performance later. :^)
