QueryEngine: Calculate stable hashes for Foundation.URL and FoundationEssentials.URL

Until Swift 6.0, the fully-qualified name of the URL type was
`Foundation.URL`.  After the adoption of FoundationEssentials, the
name changed to `FoundationEssentials.URL`.  This difference causes
the hashes to change, so for backwards compatibility we pin the
type name to `Foundation.URL`.

Fixes #45

Author: euanh

Sources/Helpers/Vendor/QueryEngine/CacheKey.swift

@@ -168,6 +168,12 @@ extension FilePath.Component: LeafCacheKey {
 extension URL: LeafCacheKey {
   func hash(with hashFunction: inout some HashFunction) {
     String(reflecting: Self.self).hash(with: &hashFunction)
+    
+    // Until Swift 6.0, the fully-qualified name of the URL type was `Foundation.URL`.
+    // After the adoption of FoundationEssentials, the name changed to `FoundationEssentials.URL`.
+    // This difference causes the hashes to change, so for backwards compatibility we pin the
+    // type name to `Foundation.URL`.
+    "Foundation.URL".hash(with: &hashFunction)
     self.description.hash(with: &hashFunction)
   }
 }