Added support for getters with no prefix on FieldResolver

[OwlyCode]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Documented?	no
License	MIT

When upgrading to 13.1 my API broke: all of a sudden, some fields were null instead of their actual value.

The problem is inside the FieldResolver, it does not handles methods with no leading get prefix. In my case my entity looks like this:

class Entity
{
    public function hasSomething() {
        //...
    }
}

And the schema:

Entity:
    type: object
    config:
        fields:
            hasSomething:
                type: "Boolean"
            # ...

We want to call $entity->hasSomething() during resolution, not only $entity->getHasSomething().

[mcg-web]

Thank you @OwlyCode !