This tests:
* Getter invocation
* Setter invocation
* Properties with one or the other, but not both
* Inheritance
* Superproperty getters and setters
* Getters with inherited setter
* Setters with inherited getter
The previous system for handling setters would execute the setter and then return a value to indicate whether or not the caller needed to resolve a stack frame. However, no caller of `Property.set` actually did this. Ergo, errors in setters and getters would not resolve up the stack at the correct time.
This problem also exists in AVM1 but is far less noticable as AVM1 only has two very uncommon runtime errors and very few movies use `throw`.
Normally, `set_property` only affects the object it was called on, which makes sense: otherwise, we couldn't override values that originate from a class prototype without accidentally monkey-patching the prototype. However, virtual setters only exist in prototypes and need to be accessible from child objects.
The solution to this is to have a specific method to check if a virtual setter exists. Virtual setters are then resolved through the prototype chain. If no virtual setter exists, then the reciever object is handed the value.
Note that we always use the `reciever` object rather than `self` so that `setsuper` can work correctly. In `setsuper`, we resolve the base class, and then set properties on it with the actual object in question as it's reciever. If a virtual setter is called, it will get the actual object it should be manipulating; and otherwise, prototypes will not be modified or consulted.
This required the reintroduction of dedicated reciever parameters to `Object.get_property_local` and `Object.set_property`, which I had removed from the AVM1 code I copied it from. It turns out being able to change the reciever was actually necessary in order to make super set/get work.
The previous system primarily relied on `Executable` to automatically start and continue a super chain. This works, but only for class hierarchies without *override gaps* - methods that override another method not defined by the direct superclass of the method. In that case, the override method would be called twice as the `base_class` was moved up one prototype at a time, which is wrong.
The new system relies on the call site to accurately report the prototype from which the current method was retrieved from. Super calls then start the resolution process *from the superclass of this prototype*, to ensure that the already-called method is skipped.
It should be noted that the proper `base_class` for things like `callmethod`, `callstatic`, `call`, `get`/`set` methods, and other call opcodes that don't use property look-up are best-effort guesses that may need to be amended later with better tests.
To facilitate `base_proto` resolution, a new `Object` method has been added. It's similar to `get_property`, but instead returns the closest prototype that can resolve the given `QName`, rather than the actual property's `ReturnValue`. Call operations use this to resolve the `base_proto`, and then resolve the method being called in `base_proto`. The existing `exec_super` method was removed and a `base_proto` method added to `exec` and `call`.
This works primarily by retaining the current superclass prototype in the activation object and then using it to retrieve the super method.
For constructors, we implement the `constructor` property, which is probably not the correct way to do this.
This currently treats `coerce_a` as a no-op. Strictly speaking, this is for type verification purposes, but we currently don't type-verify ABC code. Ergo, this requires no VM support at this time.
Also, implement a method table that method traits can optionally add themselves to.
Also also, add the ability to invoke a method without a `this` object. This required a non-trivial refactoring of the activation machinery, and changes to the signature of `NativeFunction`, and all native AVM2 functions.
In the future, the `unwrap_stack_frame` mechanism should be expanded upon to allow running exception handlers and recovering from a Rust error - but not today.
Notably, this also removes `new_closure_scope` as it is not needed. AVM1 does not capture `with` scopes in closures, but AVM2 (as well as modern ECMAScript) does.
We already have a menagerie of `install_*` functions for adding static properties to a an object; and we don't have to support any kind of asinine nonsense liks `ASSetPropFlags` here. Ergo, we don't need this.
In AVM1, these are necessary because `ActionGetVariable` et. all directly interface with the scope chain. In AVM2, you `findpropstrict` up the scope chain, which gives you a normal object that you can interact with as you like. Ergo, the scope chain doesn't need set/get property methods.
David Wendt