Extension getter/setter prevents error from being reported for missing setter/getter on function type

[stereotype441]

The analyzer accepts the following code, but the CFE rejects it:

extension on Object? {
  int get foo => 0;
}

test(void Function() f) {
  f.foo = 0; // ERROR
}

The CFE is correct in rejecting the code; there is no .foo= setter defined for the type void Function().

A similar thing happens with the roles of the getter and setter reversed. Again, the analyzer accepts the code, but the CFE rejects it:

extension on Object? {
  set foo(int value) {}
}

test(void Function() f) => f.foo; // ERROR
``
Again, the CFE is correct in rejecting the code.

[stereotype441]

I'm going to work on this.