Do not send the 'body' field for DAP Initialized Event. (#1345)

The body field is required on most DAP Events and optional on Terminated but
is actually not included in Initialized at all. Clients parsing the Events
strictly will think an Initialized Event with a body is malformed, so this
change drops the field entirely for Initialized.

https://microsoft.github.io/debug-adapter-protocol/specification#Events_Initialized

apps/els_dap/src/els_dap_protocol.erl

@@ -30,8 +30,16 @@
 %%==============================================================================
 %% Messaging API
 %%==============================================================================
--spec event(number(), binary(), any()) -> binary().
-%% TODO: Body is optional
+
+-spec event(number(), binary(), map()) -> binary().
+event(Seq, <<"initialized">> = EventType, _Body) ->
+    %% The initialized event has no body.
+    Message = #{
+        type => <<"event">>,
+        seq => Seq,
+        event => EventType
+    },
+    content(jsx:encode(Message));
 event(Seq, EventType, Body) ->
     Message = #{
         type => <<"event">>,