systemd/gnome-session: move gnome-shell session files into subpackage

Just some change we already have upstream for a while but forgot to copy
over here downstream

Ref: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/79185

Part-of: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/6520
[ci:skip-build]: already built successfully in CI

extra-repos/systemd/gnome-session/APKBUILD

@@ -3,7 +3,7 @@
 pkgname=gnome-session
 pkgver=99948.0
 _pkgver=48.0
-pkgrel=0
+pkgrel=1
 pkgdesc="GNOME session manager"
 url="https://gitlab.gnome.org/GNOME/gnome-session"
 arch="all"
@@ -32,7 +32,7 @@ makedepends="
 options="!check" #no tests
 # FIXME: _shell subpackage is not in this forked package because pmbootstrap
 # currently can't handle it: https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/merge_requests/2592
-subpackages="$pkgname-lang $pkgname-doc $pkgname-systemd"
+subpackages="$pkgname-lang $pkgname-doc $pkgname-systemd gnome-shell-session:_shell:noarch"
 source="https://download.gnome.org/sources/gnome-session/${_pkgver%%.*}/gnome-session-$_pkgver.tar.xz
 	gnome-session-bash-login.patch"
 builddir="$srcdir/gnome-session-$_pkgver"
@@ -53,6 +53,20 @@ package() {
 	DESTDIR="$pkgdir" meson install --no-rebuild -C output
 }
 
+_shell() {
+	# For other consumers of gnome-session (e.g. phosh) these session files
+	# only confuse display managers as gnome-shell isn't installed
+
+	pkgdesc="Session files for GNOME Shell"
+	depends="$pkgname=$pkgver-r$pkgrel gnome-shell"
+	install_if="$pkgname=$pkgver-r$pkgrel gnome-shell"
+
+	amove usr/share/gnome-session/sessions
+	amove usr/share/wayland-sessions
+	amove usr/share/xsessions
+	amove usr/share/xdg-desktop-portal
+}
+
 sha512sums="
 84baafdf0d7a4f4b15faaacde02821f6449481d655c8d6ff6ea79996aa052483475c9a77a021d47001249c6c84c66be728f683a2b1725657b329c64fc7951dc0  gnome-session-48.0.tar.xz
 ff14a97f16aa4ad22122c7dda181d995ee54882132800c5e766bba8203ae2851e22e4bea39fc04b5c4c34b618babc3efb2a3699a2be722b1ea962210b30e0b50  gnome-session-bash-login.patch