Changes SharedFunctionInfo to store a function_token_offset, relative
to the start_position, instead of the full function_token_position.
This enables us to reduce both FunctionTokenPosition and
ExpectedNofProperties to 16 bits each, saving 32 bits per SFI.

BUG=chromium:818642,chromium:783853
TBR=yangguo@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I45aefcec605c1da502053c23c73564ceaed6c9b5
Reviewed-on: https://chromium-review.googlesource.com/1122982
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54220}