Ignore empty fixture directories and fix fixtures in the parser

[danez]

Q	A
Fixed Issues?
Patch: Bug Fix?	y
Major: Breaking Change?	n
Minor: New Feature?	n
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

Okay this PR started because I was annoyed that sometimes when I added fixtures somewhere but then ended up reverting, the empty folder was keep but the fixture runner was still generating an output.js.

So I went in and changed the behavior of the fixture runner to ignore folders if there is neither input.ext nor exec.js. This is the first commit.

I checked which folders are ignored and noticed that there are some test fixtures in babylon which are never executed because the folder structure was wrong or the files were named incorrectly.

I fixed all of these cases which are in the second commit.

I noticed another potential issue with regular expressions where we do not check if character ranges are valid, but I did not want to dive into this one yet. So the tests for this are currently skipped.

var x = /[\u0063-b]/u; // should error I think

---

I removed the other change and moved it into a PR #9114

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/9516/

[nicolo-ribaudo]

(I did only review the first commit)