Use proper autoscale value for splash screen scaling

The splash screen is initialized by the Equinox native launcher such
that when the Workbench takes it over, the autoscaling settings used for
processing it must fit to avoid a wrongly sized background image and
controls.
Since the autoscaling default used to be "integer" and any other value
was only defined by a system property, reading that system property was
sufficient. With the adaptation of SWT and Equinox to default to
autoscaling mode "quarter" on Windows when monitor-specific scaling is
used, reading the system property is not sufficient anymore as it also
depends on whether monitor-specific scaling is enabled.

This change adapts the identification of the proper autoscaling mode by
just reading it from the SWT configuration. This also ensure that it
will be resilient against potential future changes of default settings.

Author: HeikoKlare

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/Workbench.java

@@ -3666,14 +3666,12 @@ protected String createId() {
 	}
 
 	private static class AutoscaleAdaptation {
-		private static final String SWT_AUTOSCALE = "swt.autoScale"; //$NON-NLS-1$
-
 		private boolean incompatibleMonitorSpecificScalingDisabled;
 
 		private final String initialAutoScaleValue;
 
 		public AutoscaleAdaptation() {
-			initialAutoScaleValue = System.getProperty(SWT_AUTOSCALE);
+			initialAutoScaleValue = DPIUtil.getEffectiveAutoScaleValue();
 		}
 
 		public void runWithInitialAutoScaleValue(Runnable runnable) {