The function InstanceBuilder::ProcessImports got long and hard to
understand. This CL is the second change of a series which aims at
extracting parts of ProcessImports into specialized functions.

This CL extracts the processing of imported tables into a separate
function. Aside from copying the code, I made the following changes:
* Rename {index} to {import_index}.
* Rename {table_num} to {table_index}.

R=clemensh@chromium.org

Bug: v8:8562
Change-Id: I37398f0c8feccae3647a7817d7d4d6d0d87fd5a9
Reviewed-on: https://chromium-review.googlesource.com/c/1382470
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58341}