Also test separator unified path

[tlserver]

Since ESLint return the path in os format, so ignore regexp need to handle both \ and / as a separator. Consider this rule:

{
  regex: 'regA',
  files: {
    ignore: '^.*dirA/dirB/dirC/file\\.ts.*',
  },
},

It work on mac or linux, but not windows because ...\dirA\dirB\DirC\file.ts does not match ^.*dirA/dirB/dirC/file\\.ts.*. We need to change ignore regexp to ^.*dirA[\\\\/]dirB[\\\\/]dirC[\\\\/]file\\.ts.* in order to support windows also. It is hard to read and easy to forget when a developer is working on mac or linux.

Therefore, I created this PR. now regexp not only test for original path but also a "unified" path ( all \ are replaced to / ).

[gmullerb]

Ok, Got it! ✍️
I'll review your PR and add some tests.
Thank you so much! 🙏 👍