Find/Replace Overlay: correctly set scope mode

Depending on the file format, the line separators are different.
This PR allows detecting both when deciding whether to set the scoped
search mode or not when opening the Overlay with an active selection.

fixes eclipse-platform#2054

bundles/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/internal/findandreplace/overlay/FindReplaceOverlay.java

@@ -906,7 +906,7 @@ private void updateFromTargetSelection() {
 		if (initText.isEmpty()) {
 			return;
 		}
-		if (initText.contains(System.lineSeparator())) { // $NON-NLS-1$
+		if (initText.contains("\n")) { //$NON-NLS-1$
 			findReplaceLogic.deactivate(SearchOptions.GLOBAL);
 			searchInSelectionButton.setSelection(true);
 		} else {

tests/org.eclipse.ui.workbench.texteditor.tests/src/org/eclipse/ui/internal/findandreplace/FindReplaceUITest.java

@@ -291,6 +291,20 @@ public void testActivateDialogWithSelectionActive() {
 		assertThat(fTextViewer.getDocument().get(), is("text" + System.lineSeparator() + System.lineSeparator()));
 	}
 
+	private void assertScopeActivationOnTextInput(String input) {
+		openTextViewer(input);
+		fTextViewer.setSelection(new TextSelection(0, fTextViewer.getDocument().toString().length()));
+		initializeFindReplaceUIForTextViewer();
+
+		dialog.assertUnselected(SearchOptions.GLOBAL);
+	}
+
+	@Test
+	public void testSelectionOnOpenSetsScopedMode() {
+		assertScopeActivationOnTextInput("hello\r\nworld\r\nthis\r\nhas_many_lines");
+		assertScopeActivationOnTextInput("hello\nworld");
+	}
+
 	protected AccessType getDialog() {
 		return dialog;
 	}