Everywhere: Core dump => Coredump

We all know what a coredump is, and it feels more natural to refer to
it as a coredump (most code already does), so let's be consistent.

Userland/Libraries/LibCoredump/Forward.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Coredump {
+
+class Backtrace;
+class Reader;
+
+}