New ruby additions

Hi Robin,

Here's the outcome of Kawabata-san and I worked together.
* I checked how wpt/WebKit/Blink runs these tests, and adding a new file works quite well for all of them, so I went to add a new dat file rather than adding tests to tests19.dat. This might help avoiding possible conflicts, and clear separation of test results. We could go as is, move other ruby cases to this file if you want to, or merge these tests into tests19.dat, whichever up to you.
* This file has 21 test cases:
  * all combinations of rb|rt|rtc|rp followed by rb|rt|rtc|rp, 16 cases.
  * rb|rt|rtc|rp followed by other tags (span), 4 cases.
  * test if auto-close stops at the nearest ruby when they're nested, 1 case.

I'd appreciate your review, and if this looks good, it'd be superb if you could include these tests into your pull requests so that we can put all the test cases for new-ruby in a single action.

Any questions/comments/review feedback are greatly appreciated.