[turbofan] Rework Node guts to save space.

[turbofan] Rework Node guts to save space.

This reduces the storage per-Node storage from 7 words to 6 and per-edge
storage from 6 words to 4.
On average this is about 10%-15% space savings over the whole graph.

Remove the use of std::deque as the out-of-line storage for inputs.
Reduce size of Use links and use pointer arithmetic to find Node
from Use.

R=mstarzinger@chromium.org,jarin@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1150923003

Cr-Commit-Position: refs/heads/master@{#28583}