Unindentation in triple-quoted strings affected by explicitly written newline (\n)

[goretkin]

let str = "\n   yoyo"
        println("1: ")
        println("""begin line: interpolate:$str
        begin next line:""")
end

let str = "   yoyo"
        println("2: ")
        println("""begin line: interpolate:\n$str
        begin next line:""")
end

produces

1: 
begin line: interpolate:
   yoyo
begin next line:
2: 
begin line: interpolate:
   yoyo
        begin next line:

But I had expected both blocks of outputs under 1: and 2: to be the same. I did not expect "\n" (in the string) to be treated the same as \n (in the file) within a triple-quoted string.

(kind of dual error of #7165)

[JeffBezanson]

Yes, this is a bug. It happens because we do unescaping before unindenting. I ran into this fixing #34967, where the same bug prevents you from using escapes to write an invalid string with triple quotes.