std.fmt: Add {q} format specifier

[Tetralux]

q meaning "quoted", handy for printf-debugging; especially where \rs are involved.
Generally useful when writing string manipulation code.

var s: []const u8 = "hello\x00world\r\n";
std.debug.warn("Content: {q}\n", .{s});
// Content: "hello\x00world\r\n"

[ikskuh]

Sadly, this is only trivial for ASCII characters. There might be unicode spaces that should be escaped in such a string, especially stuff like U+200B (zero width space). Or we can ignore this and just display the control characters (< 0x20, 0x7F)

[LemonBoy]

According to #1358 we could use the ? specifier instead of minting a new one.

Or we can ignore this and just display the control characters (< 0x20, 0x7F)

👍

[daurnimator]

Practically a dupe of #6218

[andrewrk]

Practically a dupe of #6218

Yes this looks like a dupe of #6218.