[CSOptimizer] Fix a conditional that ignores function type parameters to look through optionals

Since parameters that have function types don't participate in
ranking, function types that are wrapped in optionals should be
excluded as well, because it's possible to overload on that and
such overloads with optional types would gain an undue advantage.

For example:

```
func test(_: (() -> Void)?) {}
func test(_: () -> Void) {}

func compute(handler: () -> Void) {
  test(handler)
}
```

Without this change the second overload would be ignored and
the first one would be an exact match.

Resolves: rdar://157234317

Author: xedin

lib/Sema/CSOptimizer.cpp

@@ -1598,7 +1598,7 @@ static void determineBestChoicesInContext(
             // FIXME: Let's skip matching function types for now
             // because they have special rules for e.g. Concurrency
             // (around @Sendable) and @convention(c).
-            if (paramType->is<FunctionType>())
+            if (paramType->lookThroughAllOptionalTypes()->is<FunctionType>())
               continue;
 
             // The idea here is to match the parameter type against

test/SILOptimizer/infinite_recursion.swift

@@ -352,3 +352,11 @@ func recursionMatchingTypeArgs2<T: P, V: P>(_ t: T.Type, _ v: V.Type) {
   recursionMatchingTypeArgs2(T.self, V.self) // expected-warning {{function call causes an infinite recursion}}
 }
 
+func testNoInfiniteRecursionWithOverloadingOnOptional() {
+  func test(handler: @escaping (Bool) -> Void) {
+  }
+
+  func test(handler: ((Bool) -> Void)?) {
+    test(handler: handler ?? { _ in }) // Ok
+  }
+}