LibCore+rpcdump: Publish CObject graph to on-demand RPC socket

All programs that have a CEventLoop now allow local socket connections
via /tmp/rpc.PID and will dump a serialized JSON array of all the live
CObjects in the program onto connecting sockets.

Also added a small /bin/rpcdump tool that connects to an RPC socket and
produces a raw dump of the JSON that comes out.

Userland/rpcdump.cpp

@@ -0,0 +1,42 @@
+#include <LibCore/CEventLoop.h>
+#include <LibCore/CLocalSocket.h>
+#include <stdio.h>
+
+int main(int argc, char** argv)
+{
+    if (argc != 2) {
+        printf("usage: %s <pid>\n", argv[0]);
+        return 0;
+    }
+
+    CEventLoop loop;
+
+    int pid = atoi(argv[1]);
+
+    CLocalSocket socket;
+    auto success = socket.connect(CSocketAddress::local(String::format("/tmp/rpc.%d", pid)));
+    if (!success) {
+        fprintf(stderr, "Couldn't connect to PID %d\n", pid);
+        return 1;
+    }
+
+    socket.on_connected = [&] {
+        dbg() << "Connected to PID " << pid;
+    };
+
+    socket.on_ready_to_read = [&] {
+        if (socket.eof()) {
+            dbg() << "Disconnected from PID " << pid;
+            loop.quit(0);
+            return;
+        }
+
+        auto data = socket.read_all();
+
+        for (int i = 0; i < data.size(); ++i)
+            putchar(data[i]);
+        printf("\n");
+    };
+
+    return loop.exec();
+}