Emit a warning for &&

[nex3]

Dart and Ruby Sass are adding a warning for &&, since it looks like a logical operator but doesn't behave like one. The text we're using is In Sass, "&&" means two copies of the parent selector. You probably want to use "and" instead.. LibSass should add the same warning.

See sass/sass#2429 and sass/sass-spec#1192.

[mgreter]

FWIW. the following doesn't emit any warning at all in ruby sass 3.5.5

.and-and {
  value: true &&&& false;
}

Forget about it, seems it doesn't emit one once the result is "cached" ...

[mgreter]

Closed via #2530