missed bash ANSI-C quotings

[e-kwsm]

https://www.gnu.org/software/bash/manual/html_node/ANSI_002dC-Quoting.html

shellcheck/src/ShellCheck/ASTLib.hs

Lines 407 to 431 in 766a836

	decodeEscapes ('\\':c:cs) =
	case c of
	'a' -> '\a' : rest
	'b' -> '\b' : rest
	'e' -> '\x1B' : rest
	'f' -> '\f' : rest
	'n' -> '\n' : rest
	'r' -> '\r' : rest
	't' -> '\t' : rest
	'v' -> '\v' : rest
	'\'' -> '\'' : rest
	'"' -> '"' : rest
	'\\' -> '\\' : rest
	'x' ->
	case cs of
	(x:y:more) | isHexDigit x && isHexDigit y ->
	chr (16*(digitToInt x) + (digitToInt y)) : decodeEscapes more
	(x:more) | isHexDigit x ->
	chr (digitToInt x) : decodeEscapes more
	more -> '\\' : 'x' : decodeEscapes more
	_ | isOctDigit c ->
	let (digits, more) = spanMax isOctDigit 3 (c:cs)
	num = (parseOct digits) `mod` 256
	in (chr num) : decodeEscapes more
	_ -> '\\' : c : rest

Here the followings are missed:

• \E: An escape character (not in ANSI C)
• \?: question mark
• \uHHHH: The Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
• \UHHHHHHHH: The Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
• \cx: A control-x character