[ValueSerializer] Allow wire format versions beginning with 13 to be deserialized in non-legacy mode.

As of version 13, delegates do not need to worry about colliding tags with the
tags reserved by v8, since v8 inserts a "host object" prefix beforehand. Thus
the format is now suitable for more general use, without opting into the "legacy"
mode that had this caveat.

Review-Url: https://codereview.chromium.org/2722213002
Cr-Commit-Position: refs/heads/master@{#43521}