Private method loads are compiled to a named load of a private brand,
which always loads a BlockContext. This BlockContext holds the private
methods common to all instances of a class. TurboFan currently considers
JSLoadNamed to be of Type::NonInternal(). Private methods break this
assumption, since BlockContext is of Type::OtherInternal().

This CL changes the typing of JSLoadNamed of private brands to be
Type::OtherInternal().

Bug: v8:12500
Change-Id: I91f39747bf9422bd419d299f44152f567d8be8db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3351167Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78431}