For memory tracing, output a 'T' for Turbofan code and an 'L' for
Liftoff code. To do this, the WasmCodeWrapper now has some dispatch
functions which work for both on-the-heap and off-the-heap code.
We can probably refactor more code by having this mechanism.

Since the output of --wasm-trace-memory differs now between Turbofan
and Liftoff, the message test is split in two.

R=titzer@chromium.org
CC=mstarzinger@chromium.org

Bug: v8:6600
Change-Id: Ic5fd18c631f5c8aaad19d639df75b18098895b5a
Reviewed-on: https://chromium-review.googlesource.com/868214Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50655}