AK: Make it possible to move and copy HashMap and HashTable.

Previously it was only possible to move them, but we should allow copying
as well, since it's gonna be useful for many things.

AK/HashMap.h

@@ -34,19 +34,6 @@ private:
 public:
     HashMap() {}
 
-    HashMap(HashMap&& other)
-        : m_table(move(other.m_table))
-    {
-    }
-
-    HashMap& operator=(HashMap&& other)
-    {
-        if (this != &other) {
-            m_table = move(other.m_table);
-        }
-        return *this;
-    }
-
     bool is_empty() const { return m_table.is_empty(); }
     int size() const { return m_table.size(); }
     int capacity() const { return m_table.capacity(); }

AK/HashTable.h

@@ -22,7 +22,23 @@ private:
 
 public:
     HashTable() {}
-    explicit HashTable(HashTable&& other)
+    HashTable(const HashTable& other)
+    {
+        ensure_capacity(other.size());
+        for (auto& it : other)
+            set(it);
+    }
+    HashTable& operator=(const HashTable& other)
+    {
+        if (this != &other) {
+            clear();
+            ensure_capacity(other.size());
+            for (auto& it : other)
+                set(it);
+        }
+        return *this;
+    }
+    HashTable(HashTable&& other)
         : m_buckets(other.m_buckets)
         , m_size(other.m_size)
         , m_capacity(other.m_capacity)