Move v0 things from ShadowRootRareData into ShadowRootRareDataV0

It is uncomfortable that we are mixing data for v0 and v1 in one place, ShadowRoot (and ShadowRootRareData).
It is nice to separate them cleanly.

This CL introduces ShadowRootRareDavaV0 and move some of data into it.
I'll do another clean up in follow-up CLs, moving some of data in ShadowRoot into ShadowRootRareDataV0.

BUG=531990

Review URL: https://codereview.chromium.org/1904703002

Cr-Commit-Position: refs/heads/master@{#388718}
5 files changed