css-minifier: some compression rules fail when `@keyframes` are inside `@layer`

[yisibl]

@layer foo {
  @keyframes     slide-left    {
    from   { width: 200px; }
    100%   { width: 500px; }
  }
}

esbuild output:

@layer foo{@keyframes slide-left {from {width: 200px;} 100% {width: 500px;}}}

Expectation

No problem when there is no @layer. https://caniuse.com/mdn-css_at-rules_layer

@layer foo{@keyframes slide-left{0%{width:200px}to{width:0}}}

[evanw]

This is a new CSS rule so esbuild doesn't know about it yet. I can add basic support for it.