[Fix #1263] Do not report %W literals with special characters

Just like `%W` literals with interpolation can not be changed to `%w`, special escaped characters like `\0000` would also change meaning if changing to lower case `%w`.

There was an invalid spec example for auto-correct. The character sequence `?\n` inside `%W` means a question mark followed by a newline. It's special and should not be reported or auto-corrected.