feature: intercept object access

[talss89]

It should be possible to intercept calls / accesses made by a handler to $this, without replacing the original handler.

This means we can register on_call type events that are fired when a filter / action handler tries to access it's own $this. We can then either return a new value to skip execution of the $this->some_method() call, or return null to allow the call to continue.

This is a huge rabbit hole, and will need some thought. In theory we could pre and post process any object accessor similar to how we inject().

• Create event trigger / handler subsystem
• Intercept object method calls
• Override and skip object method calls
• Intercept property accesses
• Intercept property writes
• Recursive HookProxy works (ie. proxying-a-proxy should proxy the original object)

Branch feature/intercept tracks this feature.

[talss89]

May need to refactor HookProxy a bit for this. Detecting calls doesn't require a proxy, but detecting property access does.

Need to ensure HookProxy can proxy another HookProxy recursively too. Unsure if this works currently - not tested.

[talss89]

Recursive HookProxy test now in branch, and is passing.

    public function testRecursiveProxy() {
        $obj = new MockClass(3);
        $proxy_1 = new HookProxy(function($input) {return $input . '-proxy_1';}, $obj);
        $proxy_2 = new HookProxy(function($input) {return $input . '-proxy_2' . '-' . $this->{'id'};}, $proxy_1);

        $this->assertEquals("test-proxy_2-3", $proxy_2->___cb("test"));
    }
}