This CL introduces an stack abstraction for writing frame descriptions.
Previously, we managed the output offset by hand, which is verbose and
error prone. This CL introduced FrameWriter, which offers a stack
abstraction with push operations for constructing the output frame
descriptions.

The abstraction is only applied to DoComputeBuiltinContinuation;
following CLs will apply it to the other DoCompute* functions.

Bug: v8:7679

Change-Id: Ia6e34de1ed63ba9245e2a08945b1e0548562ed43
Reviewed-on: https://chromium-review.googlesource.com/1019143Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52714}