in string interpolation in multiline string literal.
"""
\("<-this is unterminated.
"""
In this case, the outer multiline literal should form 'tok::unknown'
along with a error message.
Maintain inner most string literal mode to determine whether we allow
newline character or not.
* Disallow newline after multiline string in string interpolation. (SR-5171)
* Allow unbalanced `"` in multiline string in string interpolation.
This adds support for SE-0168, multi-line string literals.
Extend the lexer to recognize the new literals. Test cases added.
There are still areas for future diagnostic improvement, such as fixits and notes as to why a multi-line string literal will be malformed. Multi-line literals are explicitly forbidden inside of string interpolation, though this may be relaxed in the future.
