See the WebAssembly bulk memory proposal here:
https://github.com/WebAssembly/bulk-memory-operations

This initial CL adds a wasm experimental flag:
`--experimental-wasm-bulk-memory`, and also parsing of passive segments.

A passive segment is one that is not copied into the table/memory on
instantiation, but instead later via the `{table,memory}.init`
instructions.

The binary format of passive data segments is unlikely to change, but
the format for passive element segments may change (see
https://github.com/WebAssembly/bulk-memory-operations/pull/39).

Bug: v8:7747
Change-Id: I2a7fb9bc7648a722a8c4aab4185c68d3d0843858
Reviewed-on: https://chromium-review.googlesource.com/c/1330015
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57451}