If a bound function is passed as argument to
d8.test.verifySourcePositions, unwrap the bound target function.

Bug: chromium:1186491
Change-Id: I619cb27d19166e2dc59f3fda1e2324598640b04a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2778275
Auto-Submit: Patrick Thier <pthier@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73598}