Revert "Bug 567543 - Replace usage of Platform.getAdapterManager().getAdapter()"

This reverts commit 279714b4e046f89c2c4f0e30d10f5e3e97ac1661.

Reason for revert: Bug 572904.
IAdaptable should never delegate getAdapter() call to Adapters, 
this can lead to recursion and stack overflow.

Change-Id: I9171a0ddfcd923d64e1f725fd670a8f29c2a8721
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/179031
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>
diff --git a/bundles/org.eclipse.ui.workbench/Eclipse UI/org/eclipse/ui/internal/PartSite.java b/bundles/org.eclipse.ui.workbench/Eclipse UI/org/eclipse/ui/internal/PartSite.java
index 1e8193d..3d8c9fc 100644
--- a/bundles/org.eclipse.ui.workbench/Eclipse UI/org/eclipse/ui/internal/PartSite.java
+++ b/bundles/org.eclipse.ui.workbench/Eclipse UI/org/eclipse/ui/internal/PartSite.java
@@ -18,8 +18,8 @@
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
-import org.eclipse.core.runtime.Adapters;
 import org.eclipse.core.runtime.IConfigurationElement;
+import org.eclipse.core.runtime.Platform;
 import org.eclipse.e4.core.contexts.ContextFunction;
 import org.eclipse.e4.core.contexts.IEclipseContext;
 import org.eclipse.e4.ui.model.application.MApplication;
@@ -570,7 +570,7 @@
 			return adapter.cast(new WorkbenchPartTestable(this));
 		}
 
-		return Adapters.adapt(this, adapter);
+		return Platform.getAdapterManager().getAdapter(this, adapter);
 	}
 
 	public void activateActionBars(boolean forceVisibility) {