devtools: Handle the setBreakpoint message. (#41925)

Listen for `setBreakpoint` on `debugger.js` and add the relevant WebIDLs
and Servo counterparts to trigger this event and notify SpiderMonkey.

Implement `find_source` for `SourceManager` and `find_offset` for
`SourceActor`.

Testing: Manual testing and `./mach test-devtools` (note, the latter
seems to have some failing tests, we are investigating this, but this
patch doesn't add any new failure).
Fixes: Part of #36027

---------

Signed-off-by: eri <eri@igalia.com>
Co-authored-by: atbrakhi <atbrakhi@igalia.com>

components/script_bindings/webidls/DebuggerSetBreakpointEvent.webidl

@@ -0,0 +1,12 @@
+/* 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 DebuggerSetBreakpointEvent : Event {
+    readonly attribute unsigned long spidermonkeyId;
+    readonly attribute unsigned long scriptId;
+    readonly attribute unsigned long offset;
+};