Local declarations were previously encoded as an optional set of
4 uint16 values as part of the function declaration. This CL
implements the current design of moving these declarations to
a list of pairs of (type, count) that is part of the body.

R=bradnelson@chromium.org,binji@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1763433002

Cr-Commit-Position: refs/heads/master@{#34564}