AK: Turn ByteBuffer into a value type

Previously ByteBuffer would internally hold a RefPtr to the byte
buffer and would behave like a reference type, i.e. copying a
ByteBuffer would not create a duplicate byte buffer, but rather
two objects which refer to the same internal buffer.

This also changes ByteBuffer so that it has some internal capacity
much like the Vector<T> type. Unlike Vector<T> however a byte
buffer's data may be uninitialized.

With this commit ByteBuffer makes use of the kmalloc_good_size()
API to pick an optimal allocation size for its internal buffer.

Kernel/CMakeLists.txt

@@ -256,7 +256,6 @@ set(KERNEL_SOURCES
 )
 
 set(AK_SOURCES
-    ../AK/ByteBuffer.cpp
     ../AK/FlyString.cpp
     ../AK/GenericLexer.cpp
     ../AK/Hex.cpp