Make `__invoke()` shorthand work with static return types

<?php

class C {
    /**
     * @return static
     * (or (at)return $this)
     */
    public function g() {
        return $this;
    }

    /**
     * @return static
     */
    public function __invoke(...$args) {
        var_export($args);
        return $this;
    }
}

class D extends C {
    public function methodOfD() {
    }
}
class E extends D {
    public function methodOfE() {
    }
}

$e = new E();
echo $e->g()->methodOfD();
echo $e->g()->methodOfE();
echo $e->g()->undeclaredMethod();  // warns
echo $e()->methodOfD();
echo $e()->methodOfE();
echo $e()->undeclaredMethod();  // should warn, but doesn't yet
echo $e->__invoke()->undeclaredMethod();  // warns

EDIT(2019-01-06): This incorrectly emits PhanContextNotObject Cannot access static when not in object context

Start with the reproducer in this issue and trace how Phan handles the __invoke() shorthand and @return static annotations. Add or update a regression test so calls through $e() report undeclared methods like direct __invoke() calls, without emitting the incorrect PhanContextNotObject warning.