The format of the name section changed recently. It now contains
subsections of different type (currently for function names or local
variable names).
This CL changes our internal wasm module builders (in JS and C++) to
emit this new format, and changes the decoder to understand it.
We currently only parse the function name section, and ignore names of
local variables. I will later extend this to parse local variable names
when needed for debugging.

R=ahaas@chromium.org, rossberg@chromium.org
BUG=v8:6222

Change-Id: I2627160c25c9209a3f09abe0b88941ec48b24434
Reviewed-on: https://chromium-review.googlesource.com/470247
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Rossberg <rossberg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44492}