As a first step to support Fast API calls with overloads, adds a
new FunctionTemplate constructor that accepts a vector of CFunction*.

Bug: v8:11739
Change-Id: I112b1746768f52df52c893a4f1fb799b6bd90856
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2860838Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Paolo Severini <paolosev@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#74481}