feat: support skip impl generation

[WqyJh]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

Implement #1349

User Case Description

定义以下接口：

type TestSkipImpl interface {
	// gen:skip
	SkipMethod(id int) (gen.T, error)

	// NoSkipMethod
	// select * from users where id=@id
	NoSkipMethod(id int) (gen.T, error)
}

在生成的接口中会包含两个接口函数

type IUserDo interface {
	// ......
	SkipMethod(id int) (result model.User, err error)
	NoSkipMethod(id int) (result model.User, err error)
}

但是只会生成一个实现函数

// NoSkipMethod
// select * from users where id=@id
func (u userDo) NoSkipMethod(id int) (result model.User, err error) {
	var params []interface{}

	var generateSQL strings.Builder
	params = append(params, id)
	generateSQL.WriteString("select * from users where id=? ")

	var executeSQL *gorm.DB
	executeSQL = u.UnderlyingDB().Raw(generateSQL.String(), params...).Take(&result) // ignore_security_alert
	err = executeSQL.Error

	return
}