Add a C++ helper function called "CreateBoundFunction" as a static
function to the Intl class, and change all existing builtins involving
the creation of a bound function to use it instead.

Also remove the redundant ContextSlot enums on all Intl objects in favor
of a single BoundFunctionContextSlot enum in the Intl class.

Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: Ibd541f5e79828cd1e2cd573a0e23fc93b348a8ad
Reviewed-on: https://chromium-review.googlesource.com/1194817
Commit-Queue: Ujjwal Sharma <usharma1998@gmail.com>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55508}