AK: Allow to clear HashTables/Maps with capacity

Author: https://github.com/Hendiadyoin1
Commit: https://github.com/SerenityOS/serenity/commit/f76241914c8
Pull-request: https://github.com/SerenityOS/serenity/pull/10723

AK/HashMap.h

@@ -46,6 +46,7 @@ public:
     [[nodiscard]] size_t size() const { return m_table.size(); }
     [[nodiscard]] size_t capacity() const { return m_table.capacity(); }
     void clear() { m_table.clear(); }
+    void clear_with_capacity() { m_table.clear_with_capacity(); }
 
     HashSetResult set(const K& key, const V& value) { return m_table.set({ key, value }); }
     HashSetResult set(const K& key, V&& value) { return m_table.set({ key, move(value) }); }

AK/HashTable.h

@@ -255,6 +255,21 @@ public:
     {
         *this = HashTable();
     }
+    void clear_with_capacity()
+    {
+        if constexpr (!Detail::IsTriviallyDestructible<T>) {
+            for (auto* bucket : *this)
+                bucket->~T();
+        }
+        __builtin_memset(m_buckets, 0, size_in_bytes(capacity()));
+        m_size = 0;
+        m_deleted_count = 0;
+
+        if constexpr (IsOrdered)
+            m_collection_data = { nullptr, nullptr };
+        else
+            m_buckets[m_capacity].end = true;
+    }
 
     template<typename U = T>
     ErrorOr<HashSetResult> try_set(U&& value, HashSetExistingEntryBehavior existing_entry_behavior = HashSetExistingEntryBehavior::Replace)