Support Shadow DOM >>> operator

New Shadow DOM syntax for /deep/ does not work properly in everything-but-compressed mode:

.foo >>> .bar {
  color: red;
}

Expected:

.foo >>> .bar {
  color: red;
}

Result:

.foo > > > .bar {
  color: red;
}

I don’t know if the spaces between operators are relevant or not, but the specs mention >>> as a whole, so Sass should probably stick to this. Or at least print it as authored, rather than spacing them all.

[nex3]

I just talked to @tabatkins and it sounds like this is going to be pulled from the spec.

[tabatkins]

>>> won’t be pulled from the spec, but it is limited to just the static profile (which doesn’t include stylesheets). So it’s inappropriate for Sass to support it, as it’s effectively an invalid selector in this context.