Add dev-qt from an older version of the gentoo repo

Qt5 has been removed, we restore it since we still use it.

dev-qt/qtshadertools/qtshadertools-6.9999.ebuild

@@ -0,0 +1,17 @@
+# Copyright 2021-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+inherit qt6-build
+
+DESCRIPTION="Qt APIs and Tools for Graphics Pipelines"
+
+if [[ ${QT6_BUILD_TYPE} == release ]]; then
+	KEYWORDS="~amd64 ~arm ~arm64 ~hppa ~loong ~ppc ~ppc64 ~riscv ~x86"
+fi
+
+RDEPEND="
+	~dev-qt/qtbase-${PV}:6[gui]
+"
+DEPEND="${RDEPEND}"