Add codegen support for up to 4GiB memories in Liftoff code.

This CL also adds three new mjsunit tests that stress large WASM
memories (1, 2, and 4 GiB) and checks that accesses near these
boundaries properly generate traps.

Note there is still some trickiness around the setting of:
  1.) the flag --wasm-max-mem-pages
  2.) wasm-limits.h kSpecMaxWasmMemoryPages = 65536
  3.) wasm-limits.h kV8MaxWasmMemoryPages = 32767

In particular, the allocation of memories is still limited to
3.) and the runtime flag can only lower this limit.

The above means that the tests for 2GiB and 4GiB memories will silently
OOM by design until 3.) is changed (though they currently pass with
manual testing). I argue it is better to include these tests up front,
since they will immediately trigger if their memory allocation succeeds.

Therefore the plan is to lift the restriction on 3.) after removing
all other other internal V8 limitations including array buffers and views.

R=clemensh@chromium.org
CC=mstarzinger@chromium.org
BUG=v8:7881

Change-Id: I3205ac2daf5c9a84364c670a2c3ef2258e5649f6
Reviewed-on: https://chromium-review.googlesource.com/1151309
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54754}