Unused boolean statements

[srawlins]

Accidental == instead of = can be caught when used as a statement.

Basically I think #11625 should be a lint rather than an analyzer warning.

void main() {
  var a = 1;
  var b = 2;
  a == 2; // lint here.
}

[pq]

@bwilkerson : I see your name is on #11625 ... do you agree that this should be a lint not a hint?

[bwilkerson]

Yes. It feels more like a lint than a hint.

[srawlins]

This is covered by unnecessary_statements.