[Go] bug fix (breaking), minor code format enhancement

[wing328]

• bug fix for required parameters in the parent class. Example (breaking as this bug fix changes the method signature)
• minor code format enhancement

cc @antihax (2017/11) @grokify (2018/07) @kemokemo (2018/09) @jirikuncar (2021/01)

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[therve]

Hi, this breaks our generation in a few small cases due to the change in model_simple. It looks like requiredVars and allVars don't handle nullables correctly, we end up with invalid types like Newbool and Newint64 instead of NewNullableBool and NewNullableInt64. Wondering if you have an idea.

Edit: #8820 I think.