Feature: support finding method declared by metaClass

IntelliJ IDEA knows that the `b` method used in `a.b()` is defined in `A.metaClass.b = {}`.

```groovy
class A {
    def a() {
        return 1
    }
}


A.metaClass.b = {
    return 2
}

def a = new A()

println a.a()
println a.b()
```

It would be nice if the Groovy language server could support this feature.
