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.

AK/Forward.h

@@ -10,8 +10,13 @@
 
 namespace AK {
 
-class Bitmap;
+namespace Detail {
+template<size_t inline_capacity>
 class ByteBuffer;
+}
+
+class Bitmap;
+using ByteBuffer = AK::Detail::ByteBuffer<32>;
 class IPv4Address;
 class JsonArray;
 class JsonObject;