sd-event: store and compare per-module static origin id

sd-event objects use hashmaps, which use module-global state, so it is not safe
to pass a sd-event object created by a module instance to another module instance
(e.g.: when two libraries static linking sd-event are pulled in a single process).
Initialize a random per-module origin id and store it in the object, and compare
it when entering a public API, and error out if they don't match, together with
the PID.

man/sd_event_source_set_enabled.xml

@@ -127,7 +127,7 @@
         <varlistentry>
           <term><constant>-ECHILD</constant></term>
 
-          <listitem><para>The event loop has been created in a different process.</para></listitem>
+          <listitem><para>The event loop has been created in a different process, library or module instance.</para></listitem>
 
         </varlistentry>