Avoid inlining the {SmallVector::Grow} function, as it is rarely used.
This reduces binary size, since {emplace_back} is called a lot, and
often {emplace_back} itself is inlined.
As another minor tweak the {Grow} function now returns the new end of
the used storage, to reduce binary size in {emplace_back} even more.
Also, there is a separate version without argument.

R=mlippautz@chromium.org

Change-Id: If25f976649fee3f585b9a2cf6bdfe00fdb77af0b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1683995Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62467}