strconv: Unquote does not reject invalid escape sequences

[dsnet]

Considering the following snippet:

s, err := strconv.Unquote(`"\udead"`) // outputs "\ufffd", nil

This is incorrect as Unquote is supposed to parse a string literal according to the Go specification for string literals, which forbids surrogate halves. I expect this to report an error.

[gopherbot]

Change https://golang.org/cl/343877 mentions this issue: strconv: reject surrogate halves in Unquote