[Enhancement] Support instance methods.

[thargy]

Currently, calling instance methods doesn't work. To support, we need to rewrite providing the instance as the first parameter, e.g. (extending the example in #72):

    public struct SimpleConstructedStruct
    {
        public readonly float OutFloat;

        public SimpleConstructedStruct(float outFloat)
        {
            OutFloat = outFloat;
        }

        public SimpleConstructedStruct Increment()
        {
            return new SimpleConstructedStruct (OutFloat + 1.0f);
        }
    }

...
    SimpleConstructedStruct s = new SimpleConstructedStruct(1.0f);
    s = s.SimpleConstructedStruct();

Should be written as:

    struct SimpleConstructedStruct
    {
        float OutFloat;
    };

    SimpleConstructedStruct_0_ctor(float outFloat)
    {
        SimpleConsructedStruct this;
        this.OutFloat = outFloat;
        return this;
    }

    SimpleConstructedStruct_Increment(SimpleConstructedStruct this)
    {
        return SimpleConstructedStruct_0_ctor(this.OutFloat + 1.0);
    }

...
    SimpleConstructedStruct s = SimpleConstructedStruct_0_ctor(1.0);
    s = SimpleConstructedStruct_Increment(s);

[mellinoe]

Yeah, this would be very handy. Rewriting things as static functions is both annoying and slower for regular C#.