proposal: Go 2: When dealing with err, add a wildcard

[misaka123456]

  err := func()
  if err != nil {
     return errpkg.Wrap(err)
  }

can change it to
~ = fun()

相当于如果~的类型为error，并且A()的返回值为error，并且~不为nil，这自动转换为 return errpkg.Wrap(err)
Equivalent to if the type of ~ is error, and the return value of A() is error, and ~ is not nil, this is automatically converted to return errpkg Wrap(err)

for example

fun A() error {
  ~ = fun()
}
// 相当于，Equivalent to
fun A() error {
  err := func()
  if err != nil {
     return errpkg.Wrap(err)
  }
}

fun A() (user error) {
  ~ = fun()
}
// 相当于，Equivalent to
fun A() error {
  err := func()
  if err != nil {
     return nil, errpkg.Wrap(err)
  }
}

[randall77]

Dup of #42214 using a different token.