This is a first step to make {WasmCode} objects smaller. Many code
offsets are currently stored in {size_t} even though there were
originally (during assembly) an int. Others are stored in {uint32_t}.

This CL switches the function index and all code lengths and offsets to
int, because
a) bigger code is not supported anyway, and
b) the style guide recommends int over unsigned types.

This makes the {WasmCode} 24 bytes smaller on x64 (from 144 to 120
bytes).

R=ahaas@chromium.org

Bug: v8:10254
Change-Id: I8f78bf4be64d59cf9393e3b6662d9d3bd153d387
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2074217Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66462}