Port away from deprecated KIconLoader::IconSize

Summary: Use `QStyle::pixelMetrics` instead

Test Plan:
No compiler warning
Icon still happily bounces on application launch

Reviewers: #kwin, davidedmundson, broulik

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Maniphest Tasks: T11637

Differential Revision: https://phabricator.kde.org/D27726

effects/CMakeLists.txt

@@ -16,7 +16,6 @@ set(kwin_effect_KDE_LIBS
     KF5::ConfigWidgets
     KF5::GlobalAccel
     KF5::I18n
-    KF5::IconThemes
     KF5::Notifications # screenshot effect
     KF5::Plasma # screenedge effect
     KF5::WindowSystem

effects/startupfeedback/startupfeedback.cpp

@@ -27,7 +27,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QPainter>
 // KDE
 #include <KConfigGroup>
-#include <KIconLoader>
 #include <KSharedConfig>
 #include <KStartupInfo>
 #include <KSelectionOwner>
@@ -291,7 +290,7 @@ void StartupFeedbackEffect::start(const QString& icon)
     m_cursorSize = readCursorSize();
     int iconSize = m_cursorSize / 1.5;
     if (!iconSize) {
-        iconSize = IconSize(KIconLoader::Small);
+        iconSize = QApplication::style()->pixelMetric(QStyle::PM_SmallIconSize);
     }
     // get ratio for bouncing cursor so we don't need to manually calculate the sizes for each icon size
     if (m_type == BouncingFeedback)