`memory.init` copies bytes from a passive data segment to linear memory.

`memory.drop` is an instruction that informs the wasm VM that the instance no
longer needs access to the passive data segment.

Information about the passive data segments, including their contents, length,
and whether they are dropped, is stored in the `WasmInstanceObject` as primitive
arrays.

Bug: v8:7747
Change-Id: I1515c8868c9be227743456a539126c15280b5365
Reviewed-on: https://chromium-review.googlesource.com/c/1370691Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58196}