When using a shared WebAssembly.Memory, always try to reserve up to the
maximum to avoid having to move the buffer. If after multiple retries
it is not possible to reserve the maximum, fall back to initial size
reservation.

 - Add new methods to allocate a Shared WebAssemblyMemory.buffer
 - Use these to reserve upto the mazimum for a Shared WebAssembly.Memory
 - Cleanup js-api so actual allocation is done inside the constructor

BUG: v8:8564
Change-Id: I97815c7c94a2b84416cd867fb23b3c815d7f0f12
Reviewed-on: https://chromium-review.googlesource.com/c/1480910Reviewed-by: Ben Smith <binji@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59805}