Add IContextFunction.ServiceContextKey OSGi component property type

This annotation simplifies the specification of the
'service.context.key' service property for IContextFunction
implementations and makes it type-safe and more robust:
'''
@component(service = IContextFunction.class)
@IContextFunction.ServiceContextKey(IProgressService.class)
public class ProgressServiceCreationFunction extends ContextFunction {
'''

runtime/bundles/org.eclipse.e4.core.contexts/META-INF/MANIFEST.MF

@@ -1,7 +1,7 @@
 Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-SymbolicName: org.eclipse.e4.core.contexts
-Bundle-Version: 1.12.600.qualifier
+Bundle-Version: 1.13.0.qualifier
 Bundle-Name: %pluginName
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin

runtime/bundles/org.eclipse.e4.core.contexts/src/org/eclipse/e4/core/contexts/IContextFunction.java

@@ -14,7 +14,10 @@
 
 package org.eclipse.e4.core.contexts;
 
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
 import org.osgi.framework.BundleContext;
+import org.osgi.service.component.annotations.ComponentPropertyType;
 
 /**
  * A context function encapsulates evaluation of some code within an
@@ -58,9 +61,23 @@ public interface IContextFunction {
 	 * should be registered in.
 	 *
 	 * @see BundleContext#getServiceReference(String)
+	 * @see ServiceContextKey
 	 */
 	String SERVICE_CONTEXT_KEY = "service.context.key"; //$NON-NLS-1$
 
+	/**
+	 * An OSGi service component property type used to indicate the context key this
+	 * function should be registered in.
+	 *
+	 * @since 1.13
+	 * @see IContextFunction#SERVICE_CONTEXT_KEY
+	 */
+	@ComponentPropertyType
+	@Retention(RetentionPolicy.SOURCE)
+	public @interface ServiceContextKey {
+		Class<?> value();
+	}
+
 	/**
 	 * Evaluates the function based on the provided arguments and context to
 	 * produce a consistent result.