This PR fixes an issue where we didn't always generate the `@keyframes`.
Right now we only generate `@keyframes` _if_ they are being used as one
of the `--animate-*` utilities.
However, if your `--animate-*` definition is pretty long such that it is
defined across multiple lines, then we didn't always generate the
`@keyframes` for it.
This is because the animation name would look like
`'my-animation-name\n'` instead of `'my-animation-name'`.
Fixes: #16227
06dfa399e6