Even though both are allowed in the style guide, it recommends to use
'using', as its syntax is more consistent with the rest of C++.
This CL turns all typedefs in heap code to 'using' declarations.

R=mstarzinger@chromium.org

Bug: v8:8834
Change-Id: I8a9f6e1eebdd0adca4373c866e95ebab0a1e992d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1545892Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60523}