Classfile support auto-generated clone

[xushiwei]

Proposal

Provide builtin clone mechanism to replace reflection

Background

https://github.com/goplus/yap/issues/117

Workarounds

none

[xushiwei]

auto-generated code includes:

func (this *Foo) Classfname() string {
    return "Foo"
}

func (this *Foo) Classclone() any {
    _gop_ret := *this
    return &_gop_ret
}