Support Native JSObject GType for Signals and Properties
Define a new boxed 'JSObject' GType and use it to wrap native JSObject's.
To do this, create a GJSObject class that automatically roots and unroots a JSObject persistently. This class uses a private constructor and a pimpl idiom to force the allocation of the wrapper in the stack, that is doable using a 'boxed' static method that returns an unique_ptr. Internally the boxed wrapper uses a ref-counting system that allows us to avoid copies and re-rooting.
Define GObject.TYPE_JSOBJECT as 'JSObject' GType and use aliases for various JS native Objects using the $gtype property.
Add a ParamSpec jsobject alias.
- probably the rooting of the JSObject isn't that needed for my tests, since the very same pointer is always kept around when passed, from what I see, but I prefer not to any assumption of such type, unless we don't have any security over it.
- I preferred not to reuse
GjsMaybeOwned(even after a cleanup and subclassing for adding what I needed), since it would anyway add tools that we don't need.
- I commented some tests whose failures seems to be uncatchable, so any help is welcome.