fix(golang): correct receiver type resolution in selector parsing

[wzekin]

• Fix receiver type resolution by using m.Signature().Recv().Type() instead of sel.Recv()
• Add test case for struct method resolution

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fix

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修复 method call 中，receiver 解析错误的问题

• 在解析 receiver 的时候，直接使用了 sel 中的 type.Type，但如果 method 是通过引用 sub struct 调用的，此时应该返回 sub struct，而不是 sel 中的 type
• 修复后，直接使用 type.Func 中 receiver 的类型，此处的类型一定是正确的

修复前，DFunction 的 receiver 是 MyStruct
修复后，DFunction 的 receiver 是 MyStructD

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