Make quote escaping posix compliant

[harendra-kumar]

We need to make it conformant with the shell:

When inside a single quote, \ should be just like any other char, it does not escape a single quote or double quote or itself.

$ echo 'hello\\"world'
hello\\"world

When in double quote it escapes a double quote and itself only.

$ echo "hello\"\\w\'orld"
hello"\w\'orld

[adithyaov]

$ echo 'hello\'
hello\

See composewell/streamly#2397

[adithyaov]

Uncomment the failing test case after fixing this.