In the presence of default arguments, the body of the function gets
wrapped into another block. This caused our trailing-range-after-return
optimization to not apply, because the wrapper block had no source
range assigned. This CL correctly assignes a source range to that block,
which allows already present code to handle it correctly.

Note that this is not a real coverage bug; we've just been reporting
whitespace as uncovered. We're fixing it for consistency.

Originally reported on github.com/bcoe/c8/issues/66

Bug: v8:9952
Change-Id: Iab3905f558eb99126e0dad8072d03d0a312fdcd3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1903430
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64836}