GP-3 - Updated Navigatable to have a notion of selected text; updated

the SearchTextPlugin to use this feature

Ghidra/Features/ProgramDiff/src/main/java/ghidra/app/plugin/core/diff/DiffNavigatable.java

@@ -15,6 +15,8 @@
  */
 package ghidra.app.plugin.core.diff;
 
+import javax.swing.Icon;
+
 import ghidra.app.nav.*;
 import ghidra.app.plugin.core.codebrowser.CodeViewerLocationMemento;
 import ghidra.app.util.HighlightProvider;
@@ -24,8 +26,6 @@ import ghidra.program.util.ProgramSelection;
 import ghidra.util.datastruct.WeakDataStructureFactory;
 import ghidra.util.datastruct.WeakSet;
 
-import javax.swing.Icon;
-
 /**
  * This is a navigatable for use by the right-hand listing of the Diff.
  * It should navigate within the Diff's listing, which would then reposition 
@@ -140,6 +140,11 @@ class DiffNavigatable implements Navigatable {
 		return navigatable.getHighlight();
 	}
 
+	@Override
+	public String getTextSelection() {
+		return navigatable.getTextSelection();
+	}
+
 	@Override
 	public void addNavigatableListener(NavigatableRemovalListener listener) {
 		navigationListeners.add(listener);