[wildcards] produce a warning on `late` wildcard variables.

[pq]

Examples:

Initializing expression is essentially dead code:

int f() => throw StateError('unreachable');

void g() {
  late int _ = f();
  late final int _ = f();
}

Variable declaration is unnecessary (can't be accessed or assigned to):

void f() {
  late int _;
  late final int _;
}

Discussion: dart-lang/language#3798

[pq]

Similar to,

void f() {
  late int _;
  late final int _;
}

but without the late,

void f() {
  int? _;
  final int? _;
}

the _ declarations are equally dead/unnecessary.