LibWeb/IDB: Implement generate_a_key

Author: https://github.com/stelar7
Commit: dbe0db0cab
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4317
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/kennethmyhra ✅

Libraries/LibWeb/IndexedDB/Internal/KeyGenerator.h

@@ -13,13 +13,16 @@ namespace Web::IndexedDB {
 // https://w3c.github.io/IndexedDB/#key-generator-construct
 class KeyGenerator {
 public:
+    [[nodiscard]] u64 current_number() const { return m_current_number; }
+    void increment(u64 amount) { m_current_number += amount; }
+    void set(u64 value) { m_current_number = value; }
+
 private:
     // A key generator has a current number.
     // The current number is always a positive integer less than or equal to 2^53 (9007199254740992) + 1.
     // The initial value of a key generator's current number is 1, set when the associated object store is created.
     // The current number is incremented as keys are generated, and may be updated to a specific value by using explicit keys.
-    // FIXME: Implement support for KeyGenerator in ObjectStore.
-    [[maybe_unused]] u64 current_number { 1 };
+    u64 m_current_number { 1 };
 };
 
 }