libluna: Add release_data() overloads to Buffer and Vector

This can be used to transfer the underlying data to a String object without copying.

libluna/include/luna/Buffer.h

@@ -31,6 +31,8 @@ class Buffer
         return m_data;
     }
 
+    u8* release_data();
+
     u8* end()
     {
         return m_data + m_size;

libluna/include/luna/Vector.h

@@ -134,6 +134,14 @@ template <typename T> class Vector
         return m_data;
     }
 
+    T* release_data()
+    {
+        T* data = m_data;
+        m_data = nullptr;
+        m_size = m_capacity = 0;
+        return data;
+    }
+
     Slice<T> slice()
     {
         return { m_data, m_size };