This patch fixes the source panel in the DevTools that was broken due to
missing breakpoint actor implementation. The client was sending messages
to the breakpoint actor that didn't exist in Servo, resulting in
"unknown actor"
warnings in the logs(See logs in issue description)
To fix this this patch implements the `BreakpointListActor` that handles
`setBreakpoint` and `setActiveEventBreakpoints` messages with empty
replies. This PR does not implement `breakpoint` functionality
<img width="1512" alt="image"
src="https://github.com/user-attachments/assets/ac4985a6-9fd3-4854-a491-b39241e19d13"
/>
Fixes: https://github.com/servo/servo/issues/37196
Signed-off-by: atbrakhi <atbrakhi@igalia.com>
568d24d4e3