[validation-test] Adding validation test for generic function match

[LucianoPAlmeida]

Follow up to #29064
Adding a validation test from a source compatibility test that crashed.

cc @xedin

[theblixguy]

Here's a more minimised example which produces the same crash:

enum SomeEnum<T> {}

protocol FooProtocol {
  var closure: (String) -> SomeEnum<Int> { get }
}

struct ConcreteFoo<Value>: FooProtocol {
  let closure: (String) -> SomeEnum<Value>
}

[xedin]

Thank you @LucianoPAlmeida and @theblixguy! I case of validation tests - the smaller, the better and preferably without imports if possible, so if the example that @theblixguy mentioned produces the same result - let's take it.

[LucianoPAlmeida]

Humm... sure, thank you @theblixguy, @xedin :)

[xedin]

Let's update this PR and get it merged :)

[xedin]

@swift-ci please smoke test

[LucianoPAlmeida]

Tests are ok, should be good to go? :)