AK: Add HashMap::find() with customizable finder callback

This will allow clients to search the map without having to instantiate
a key value.

AK/HashMap.h

@@ -56,6 +56,11 @@ public:
     {
         return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(key, entry.key); });
     }
+    template<typename Finder>
+    IteratorType find(unsigned hash, Finder finder)
+    {
+        return m_table.find(hash, finder);
+    }
 
     ConstIteratorType begin() const { return m_table.begin(); }
     ConstIteratorType end() const { return m_table.end(); }
@@ -63,6 +68,11 @@ public:
     {
         return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(key, entry.key); });
     }
+    template<typename Finder>
+    ConstIteratorType find(unsigned hash, Finder finder) const
+    {
+        return m_table.find(hash, finder);
+    }
 
     void ensure_capacity(int capacity) { m_table.ensure_capacity(capacity); }