dev: lay the groundwork for client FS relay

Adds XDIncomingService to manage messages from another window. IPC now
registers with XDIncoming and reports whether it was handled, that way
messages intended to reach GUI can be reliably ignored.

On GUI-side, XDIncomingService will be used by FSRelayService (not yet
implemented) to handle requests for filesystem operations from another
window.

On App-side, XDIncomingService might be used by the PostMessageFS
client-side filesystem implementation terminal to listen for filesystem
events that were relayed by GUI (after a permission check) from their
original websocket source. Either that, or we'll open a filesystem
socket for each app using that app's token.

NoPuterYetService was added because IPC.js is loaded before
globalThis.puter exists, and was the easiest way to still allow IPC's
listener to be registered with XDIncomingService.

APIAccessService was added. This service currently holds auth_token and
api_token and does nothing else. FilesystemService listens to this to
maintain a websocket connection. APIAccessService will help to manage
the complexity of all further code dependent on being informed about
changes to the auth token or origin. Currently in puter.js these are
passed around to several modules which manage the same piece of state
information independantly.

src/gui/src/IPC.js

@@ -44,12 +44,12 @@ window.ipc_handlers = {};
  * 
  * Precautions are taken to ensure proper usage of appInstanceIDs and other sensitive information.
  */
-window.addEventListener('message', async (event) => {
+const ipc_listener = async (event, handled) => {
     const app_env = event.data?.env ?? 'app';
     
     // Only process messages from apps
     if(app_env !== 'app')
-        return;
+        return handled.resolve(false);
 
     // --------------------------------------------------------
     // A response to a GUI message received from the app.
@@ -61,7 +61,7 @@ window.addEventListener('message', async (event) => {
         delete window.appCallbackFunctions[event.data.original_msg_id];
 
         // Done
-        return;
+        return handled.resolve(false);
     }
 
     // --------------------------------------------------------
@@ -70,18 +70,20 @@ window.addEventListener('message', async (event) => {
 
     // `data` and `msg` are required
     if(!event.data || !event.data.msg){
-        return;
+        return handled.resolve(false);
     }
 
     // `appInstanceID` is required
     if(!event.data.appInstanceID){
         console.error(`appInstanceID is needed`);
-        return;
+        return handled.resolve(false);
     }else if(!window.app_instance_ids.has(event.data.appInstanceID)){
         console.error(`appInstanceID is invalid`);
-        return;
+        return handled.resolve(false);
     }
 
+    handled.resolve(true);
+
     const $el_parent_window = $(window.window_for_app_instance(event.data.appInstanceID));
     const parent_window_id = $el_parent_window.attr('data-id');
     const $el_parent_disable_mask = $el_parent_window.find('.window-disable-mask');
@@ -1522,4 +1524,11 @@ window.addEventListener('message', async (event) => {
             status_code,
         });
     }
+};
+
+if ( ! window.when_puter_happens ) window.when_puter_happens = [];
+window.when_puter_happens.push(async () => {
+    await puter.services.wait_for_init(['xd-incoming']);
+    const svc_xdIncoming = puter.services.get('xd-incoming');
+    svc_xdIncoming.register_filter_listener(ipc_listener);
 });