:global and :local do not work with CSS nesting #421

Description

Nested declarations in CSS combine with spaces, so I would expect the following to work:

.scopedClass {
  :global {
    .globalClass {...}
  }
}

In this case, I'd expect scopedClass to be hashed and globalClass to be left unchanged, because the selector should be equivalent to .scopedClass :global .globalClass (the selector-less block left over is debatable but it seems like the easiest approach):

.scopedClass_1t7w5_1 {
  {
    .globalClass {...}
  }
}

However, in practice, CSS Modules does not recognize the global scope for the nested class and hashes both scopedClass and globalClass:

.scopedClass_1t7w5_1 {
  {
    .globalClass_1t7w5_2 {...}
  }
}

Use-case

If this worked, it could be an extremely useful feature for working with UI from external libraries. I could apply a hashed container class around the entire component, then apply unhashed styles within the component, thus encapsulating my styling with no repetition. Take CodeMirror as an example:

.codeMirrorContainer :global {
  .cm-editor {...}

  .cm-line {...}

  .cm-placeholder {...}
}

To make this work currently, I have to repeat global for every selector:

.codeMirrorContainer {
  :global .cm-editor {...} /* or `:global(.cm-editor)` */

  :global .cm-line {...}

  :global .cm-placeholder {...}
}