Drop whitespace-only values from list.space() - #2141

list.space() can return an empty string, which is never a real value.

list.space('\r')                    // ['']                  expected []
list.space('"a b"\r\n\r\n"c d"')    // ['"a b"', '', '"c d"'] expected ['"a b"', '"c d"']

list.split() checks current !== '' before it trims, so the check is looking at a different string from the one it pushes. A chunk made only of whitespace that isn't one of the separators is not empty, so it passes the check, and then trim() turns it into '' on the way into the array.

space() splits on ' ', '\n' and '\t', so a \r is exactly such a chunk. That makes the result depend on line endings: the same stylesheet gives different values on CRLF than it does on LF.

a {
  grid-template-areas:
    "a b"

    "c d";
}

Saved with LF, list.space(decl.value) gives two values. Saved with CRLF, it gives three, and the middle one is empty.

This is the other half of #2134. That one was about comma() dropping empty values it should keep; the note there was that whitespace hides the problem because ' ' survives the emptiness check and is trimmed afterwards. The same untrimmed check leaks a value here instead of dropping one, so trimming before the check settles both directions.

comma() passes last = true and short-circuits ahead of the emptiness check, so nothing about it changes, including list.comma('a,,b') and list.comma('a, ,b') still matching.

Three assertions added; all three fail on main and pass here. Full pnpm unit is green at 699 tests, plus eslint and check-dts.