[CSOptimizer] Exclude existential metatype candidates from paramType->isAny fast path

Refines the check to guard against existential metatypes, which would cause 'Any' to sometimes
outrank 'Any.Type' candidates.

Resolves #85020

Author: clackary

lib/Sema/CSOptimizer.cpp

@@ -1429,11 +1429,13 @@ static void determineBestChoicesInContext(
         }
       }
 
-      // If the parameter is `Any` we assume that all candidates are
-      // convertible to it, which makes it a perfect match. The solver
-      // would then decide whether erasing to an existential is preferable.
-      if (paramType->isAny())
-        return 1;
+      // If the parameter is `Any`, it's generally a perfect match, except
+      // when the candidate is an existential metatype. In that case, it would
+      // cause (T.Type) -> (Any) disjunctions to outrank (T.Type) -> (Any.Type).
+      if (paramType->isAny() &&
+          !candidateType->is<ExistentialMetatypeType>()) {
+        return 1.0;
+      }
 
       // Check if a candidate could be matched to a parameter by
       // an existential opening.