This patch introduces IPC::Connection which becomes the new base class
of ClientConnection and ServerConnection. Most of the functionality
has been hoisted up to the base class since almost all of it is useful
on both sides.
This gives us the ability to send synchronous messages in both
directions, which is needed for the WebContent server process.
Unlike other servers, WebContent does not mind blocking on a response
from its client.
When waiting for a specific message, only consider messages
from the peer endpoint. Otherwise a message with the same id
for the local endpoint may be misinterpreted.
This fixes the Terminal sometimes hanging after bootup because
a local endpoint message is mistaken for the CreateMenuResponse
message.
Same issue here as we had with RefPtr and NonnullRefPtr.
Since we can't make copies of an owning pointer, we don't get quite the
same static_ptr_cast<T> here. Instead I've only added a new templated
version of OwnPtr::release_nonnull() in this patch, to solve the only
issue that popped up.
I'm not sure what the best solution here is, but this works for now.
