Before we were creating a new frame actor each time we paused, even if
the frame object in debugger.js was the same. Now we avoid this by
reusing the same frame actor id.
This helps our upcoming work on onStep, onPop, and onEnterFrame hooks.
Testing: Ran `mach test-devtools` and manually check that it works
Part of: #36027
Signed-off-by: eri <eri@igalia.com>
Co-authored-by: atbrakhi <atbrakhi@igalia.com>