Use the position of the next parameter to be declared as the end of the
initializer for default parameters, so that hole checks can be elided
for initializers using previous parameters in arrow functions.

This fixes a source of bytecode mismatches when collecting source
positions lazily.

Bug: chromium:980422, v8:8510
Change-Id: I5ab074231248b661156e7d8e47c01685448b56d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1683267Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62525}