Migrate away from the deprecated UI extensions

[ptziegler]

In several of our plugin.xml files, we use the long-deprecated extension points:

• org.eclipse.ui.editorActions
• org.eclipse.ui.actionSetPartAssociations

windowbuilder/org.eclipse.wb.core.java/plugin.xml

Lines 342 to 354 in d650c20

	<!-- ======================================================== -->
	<!-- GUI editor: our actions and commands -->
	<!-- ======================================================== -->
	<extension point="org.eclipse.ui.editorActions">
	<editorContribution targetID="org.eclipse.wb.core.guiEditor"
	id="org.eclipse.ui.texteditor.ruler.actions">
	<action definitionId="org.eclipse.wb.core.commands.switch" label="%actions.switch.name"
	tooltip="%actions.switch.text"
	class="org.eclipse.wb.internal.core.editor.actions.SwitchAction"
	menubarPath="navigate/open.ext2" helpContextId="switch_page"
	id="org.eclipse.wb.core.editor.actions.SwitchAction"/>
	</editorContribution>
	</extension>

We should try to move away from them using the following replacement extension points:

• org.eclipse.ui.menus
• org.eclipse.ui.bindings
• org.eclipse.ui.commands
• org.eclipse.ui.handlers

If possible, one might even consider using the e4 XMI fragment instead of the extension points.