There are several places where we extract function information
(instance and function index) from the deoptimization data. Add a
central method to do this.

Drive-by: Move {AttachWasmFunctionInfo} from wasm-compiler.h to
wasm-objects.h.

R=titzer@chromium.org

Change-Id: I768d2c9aa8049f75a6be02242b1fe524ff42e3e4
Reviewed-on: https://chromium-review.googlesource.com/793046Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49682}