Fix the issue with parsing @keyframes.
Also add a test case and update some test files to capture the issue with @keyframes parsing.
Add a new function `_skipToClosingBracket()` as suggested in code review.
Replace 0% and 100% selectors with `from` and `to` so that we don't use invalid 100% as tag name.
Merge pull request #8480 from adobe/rlim/at-keyframes-issue

Fix the issue with parsing @keyframes.