Don't use wildcard parameters or variables DRT-W1025

DON'T use wildcard parameters or variables.

Wildcard parameters and local variables (e.g. underscore-only names like _, __, ___, etc.) will become non-binding in a future version of the Dart language. Any existing code that uses wildcard parameters or variables will break. In anticipation of this change, and to make adoption easier, this lint disallows wildcard and variable parameter uses.

BAD:

var _ = 1;
print(_); // LINT

void f(int __) {
  print(__); // LINT multiple underscores too
}

GOOD:

for (var _ in [1, 2, 3]) count++;

var [a, _, b, _] = [1, 2, 3, 4];