In rust, there are some prefixes that may be part of the string literal.
String literals of the form b"test" (and br##"test"## etc) are byte
strings (as opposed to unicode strings), and similarly, string literals
of the form c"test" are C zero-terminated strings. Hence, added optional
prefixes to each of the string regular expressions so the prefix will be
recognized as part of the string.
Built and tested after fix.
Co-authored-by: James Corey <jc-git@neniam.net>
Highlight character literals started with a single quote (').
Importantly this ensures correct highlighting for the character literal '"'.
Limitation: rust char literals contain exactly one character, however this isn't checked by the highlighter.
Closes#2160
Use the 'regexp2' library for lookahead and lookbehind in region
start and end regular expressions to support things like closing quotes
that aren't preceded by backslashes.
