strconv: treat \x7f like the rest of ASCII when quoting

[robpike]

See https://go.dev/play/p/F4GlQBQL7UC

As mentioned in https://groups.google.com/d/msgid/golang-nuts/60ad41f0-10d6-417d-a604-6a151c357d93n%40googlegroups.com (which started a decade ago, almost)
, the 0x7f byte prints with \u not \x. That isn't incorrect, but it is inconsistent.

If it's worth fixing, it's a one-liner in strconv.appendEscapedRune

I vote for fixing it, although it could break some things. It trips over just what ASCII means, and to be honest \x7f is the ASCII rubout or del character.

[peterGo]

The Unicode Standard classifies 007F as a Control Character. The other Control Characters print as \x, 007F should print as \x.

Unicode Standard
http://www.unicode.org/versions/latest/

C0 Controls and Basic Latin
Range: 0000–007F
https://unicode.org/charts/PDF/U0000.pdf

Control character 007F  control = DELETE

[zamicol]

I wrote a larger test that prints the extended range. Everything is as I would expect except for \x7F.

https://go.dev/play/p/j_Mm9O98hnz

[gopherbot]

Change https://go.dev/cl/397255 mentions this issue: strconv: quote rune 007F as \x7f, not \u007f