Provide copy ctor and assignment operators as it turned out that they are
useful for embedders in certain scenarios when dealing with TracedGlobal
handles without finalization callbacks.

Bug: v8:9660
Change-Id: I2b04f540baeef61a0bc8329ca06b999571cbfe66
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1773250
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63439}