Clipboard: Add a key-value map alongside the clipboard storage

A clipping now consists of three things:

- The raw clip data
- A MIME type
- A key-value map (String, String) for anything you like

Services/Clipboard/Storage.h

@@ -27,6 +27,7 @@
 #pragma once
 
 #include <AK/Function.h>
+#include <AK/HashMap.h>
 #include <AK/SharedBuffer.h>
 #include <AK/String.h>
 
@@ -40,6 +41,7 @@ public:
     bool has_data() const { return m_shared_buffer; }
 
     const String& mime_type() const { return m_mime_type; }
+    const HashMap<String, String>& metadata() const { return m_metadata; }
 
     const u8* data() const
     {
@@ -55,7 +57,7 @@ public:
         return 0;
     }
 
-    void set_data(NonnullRefPtr<SharedBuffer>, size_t data_size, const String& mime_type);
+    void set_data(NonnullRefPtr<SharedBuffer>, size_t data_size, const String& mime_type, const HashMap<String, String>& metadata);
 
     Function<void()> on_content_change;
 
@@ -65,6 +67,7 @@ private:
     String m_mime_type;
     RefPtr<SharedBuffer> m_shared_buffer;
     size_t m_data_size { 0 };
+    HashMap<String, String> m_metadata;
 };
 
 }