Move polishcolor to a utils namespace and rename getusercolor

src/utils.h

@@ -0,0 +1,23 @@
+// SPDX-FileCopyrightText: 2023 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#include <QColor>
+#include <QGuiApplication>
+#include <QPalette>
+
+namespace Utils
+{
+
+/**
+ * @brief Get a color for a user from a hueF value.
+ *
+ * The lightness of the color will be modified depending on the current palette in
+ * order to maintain contrast.
+ */
+inline QColor getUserColor(qreal hueF)
+{
+    const auto lightness = static_cast<QGuiApplication *>(QGuiApplication::instance())->palette().color(QPalette::Active, QPalette::Window).lightnessF();
+    // https://github.com/quotient-im/libQuotient/wiki/User-color-coding-standard-draft-proposal
+    return QColor::fromHslF(hueF, 1, -0.7 * lightness + 0.9, 1);
+}
+}