In the process, add the bint type (which stands for Best-INTeger),
which implements Torque's idea of CSA's ParameterMode. It maps to
a different type on 32-bit (Smi) and 64-bit (intptr). There are
convert operators that are either no-ops or conversions
to-and-from Smi and intptrs on the each platform, depending on
the underlying type for bint. This allows Torque code to git most
of the benefits of ParameterMode without having to explicitly
pass around the mode, since it is almost always OptimalMode anyways.

Change-Id: I92e08adc1d79cb3e24576c96f9734aec1af54162
Reviewed-on: https://chromium-review.googlesource.com/c/1361160
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58253}