script: Rename DebuggerEvent to DebuggerAddDebuggeeEvent (#38571)

the next debugger script event, `getPossibleBreakpoints` (#37667), will
contain a single attribute `unsigned long spidermonkeyId`, so it will
have nothing in common with `addDebuggee`. this patch renames the latter
accordingly.

Testing: no behaviour changes other than the rename, so no tests needed
Fixes: part of #36027

Signed-off-by: Delan Azabani <dazabani@igalia.com>

components/script_bindings/webidls/DebuggerAddDebuggeeEvent.webidl

@@ -0,0 +1,18 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// This interface is entirely internal to Servo, and should not be accessible to
+// web pages.
+[Exposed=DebuggerGlobalScope]
+interface DebuggerAddDebuggeeEvent : Event {
+    readonly attribute object global;
+    readonly attribute PipelineId pipelineId;
+    readonly attribute DOMString? workerId;
+};
+
+[Exposed=DebuggerGlobalScope]
+interface PipelineId {
+    readonly attribute unsigned long namespaceId;
+    readonly attribute unsigned long index;
+};