ignore css keyframes animation styles

[artem-gusev-qs]

Hi! Thanks for great rule, i've already clean a lot of unused styles.

But for now css keyframes animation rules parsed incorrectly e.g.:

const useStyles = makeStyles(() => ({ 
  animatedDiv: {
    animation: '$myAnimation 1s linear',
  },
  '@keyframes myAnimation': { },
});

causes error "ESLint: Class undefined is unused(mui-unused-classes/unused-classes)", which has two problems:

1. We need to look for usage in other styles not in component (also as you see usage started with $ without '@keyframes ' prefix)
2. Class in error has 'undefined' name because '@keyframes myAnimation' is a key with Literal type which doesn't contain key.name property

For now I just add ignore because it blocks the rule usage.