Compile import wrappers during module compilation by introducing import
wrapper compilation units, the goal being to reduce instantiation time.

For each wrapper, we assume the imported function is going to be a
kJSFunctionArityMatchSloppy at instantiation time, which should be the
most common case. If the function turns out to have a different kind the
wrapper is going to be recompiled with the correct kind during instantiation.

R=ahaas@chromium.org, clemensh@chromium.org
CC=titzer@chromium.org

Bug: v8:9231
Change-Id: Ieb050b09d1c19f2a5a3e59132a1864dadb06775d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1630685
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61993}