This CL contains the following changes:
(1) Allocate memory for WasmTables in the WasmInstance.
    - We extend the WasmInstance by a FixedArray which stores
      references to the WasmTables.
(2) Rename the name of the backing store of WasmTables from `functions`
    to `elements`.
    - The name `functions` just does not fit anyref tables.
(3) Generate code with TurboFan for table.get and table.set.
(4) Extend wasm-module-builder.js to be able to generate modules with
    multiple tables.
(5) Add  mjsunit tests to test table.get and table.set.

R=mstarzinger@chromium.org

Bug: v8:7581
Change-Id: I44af4838ee7a37b394841a2f673ecae5734a4d1c
Reviewed-on: https://chromium-review.googlesource.com/c/1463519
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59529}