The ToDateString builtin now uses StringStream to format dates
instead of SNPrintF. The patch also implements a new allocator
based on SSO that's able to expand automatically.

Bug: v8:7770
Change-Id: I23e03ec06fcfc7bda1e5abb1ac82637e5c9ddc95
Reviewed-on: https://chromium-review.googlesource.com/c/1425905
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59119}