The "grow_memory" opcode was renamed to "memory.grow", and the spec
repo was updated to use kExprMemoryGrow internally instead of
kExprGrowMemory (https://github.com/WebAssembly/spec/pull/720).
This CL does the same change for v8.

Drive-by: Rename "current_size" to "memory.size", and a minor cleanup
in wasm-graph-builder.js to bring it in line with the version in the
js-api tests in the spec repo.

R=titzer@chromium.org

Change-Id: If525dba898b2c248890a616d3392c22b45f698ef
Reviewed-on: https://chromium-review.googlesource.com/c/1302057Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57089}