... and add move constructor and move assignment operator.
Also define some VirtualMemory parameters as r-values to explicitly express
that the ownership is passed from the caller to callee.

Bug: v8:8015
Change-Id: Iee27ddc844556dc7465177656b339cd1f83a3b56
Reviewed-on: https://chromium-review.googlesource.com/1213062Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55726}