bug#64451: 30.0.50; split-root-window-right ignores side windows

[Aaron Jensen]

(display-buffer "*scratch*" '(display-buffer-in-side-window . ((side . right))))
M-x split-root-window-right

I would expect the new window to be to the left of the side window (I
know this is counter-intuitive to splititng the root window, but it's
also intuitive given the nature of side windows...)

I don't know if this is intentional. I also don't know if it's a
regression as it's not behavior I remember seeing until fairly recently.

In GNU Emacs 30.0.50 (build 51, aarch64-apple-darwin22.5.0, NS
 appkit-2299.60 Version 13.4.1 (Build 22F82)) of 2023-06-25 built on
 Aarons-Laptop.local
Repository revision: e85ebb3d82466c5838e9c6836e6d8b5c8d0a7c33
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2299
System Description:  macOS 13.4.1

Configured using:
 'configure --with-ns --with-native-compilation --with-modules
 --without-dbus --without-webp --disable-ns-self-contained'

Configured features:
ACL GLIB GNUTLS JSON LCMS2 LIBXML2 MODULES NATIVE_COMP NOTIFY KQUEUE NS
PDUMPER PNG RSVG SQLITE3 THREADS TOOLKIT_SCROLL_BARS TREE_SITTER XIM
ZLIB