Add all missing tests to suite, mark abstract tests as such

AllWidgetTests was missing a bunch of tests, some of them seem not
very consequential (simple listener tests such as for example
[Test_org_eclipse_swt_custom_VerifyKeyListener](https://github.com/eclipse-platform/eclipse.platform.swt/blob/d5dc66178647fa40b14165a7b54bc3be8e013174/tests/org.eclipse.swt.tests/JUnit%20Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_VerifyKeyListener.java)

But other ones seem to test important functionality and are rather
more substantial, such as [Test_org_eclipse_swt_widgets_TreeColumn](https://github.com/eclipse-platform/eclipse.platform.swt/blob/d5dc66178647fa40b14165a7b54bc3be8e013174/tests/org.eclipse.swt.tests/JUnit%20Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_TreeColumn.java)

There are a few test classes which are super classes of other test classes
and exist to match all the SWT classes. These have been marked as abstract
so that it is obvious why they are not included. If you had try to run them
they would have mostly failed. The secondary advantage of explicitly
marking them abstract is that JDT won't run them as a test from within
Eclipse IDE.

There are three test classes that don't pass, I have added them to the
list commented out for now, but if they are easy enough to resolve I
will enable them too.

Fixes #2542

Author: jonahgraham

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/AllWidgetTests.java

@@ -23,22 +23,31 @@
 @Suite
 @SelectClasses({ //
 		// Sorted list of tests
+		// Failing test: Test_org_eclipse_swt_custom_BidiSegmentListener.class, //
 		Test_org_eclipse_swt_custom_BusyIndicator.class, //
 		Test_org_eclipse_swt_custom_CCombo.class, //
 		Test_org_eclipse_swt_custom_CLabel.class, //
 		Test_org_eclipse_swt_custom_CTabFolder.class, //
 		Test_org_eclipse_swt_custom_CTabItem.class, //
+		Test_org_eclipse_swt_custom_ExtendedModifyListener.class, //
+		Test_org_eclipse_swt_custom_LineBackgroundListener.class, //
+		Test_org_eclipse_swt_custom_LineStyleListener.class, //
 		Test_org_eclipse_swt_custom_StyleRange.class, //
 		Test_org_eclipse_swt_custom_StyledText.class, //
+		// Failing test: Test_org_eclipse_swt_custom_StyledTextContent.class, //
 		Test_org_eclipse_swt_custom_StyledTextLineSpacingProvider.class, //
 		Test_org_eclipse_swt_custom_StyledText_VariableLineHeight.class, //
 		Test_org_eclipse_swt_custom_StyledText_multiCaretsSelections.class, //
+		Test_org_eclipse_swt_custom_TextChangeListener.class, //
+		Test_org_eclipse_swt_custom_VerifyKeyListener.class, //
 		Test_org_eclipse_swt_widgets_Button.class, //
 		Test_org_eclipse_swt_widgets_Canvas.class, //
 		Test_org_eclipse_swt_widgets_Caret.class, //
 		Test_org_eclipse_swt_widgets_ColorDialog.class, //
 		Test_org_eclipse_swt_widgets_Combo.class, //
 		Test_org_eclipse_swt_widgets_Composite.class, //
+		Test_org_eclipse_swt_widgets_CoolBar.class, //
+		// Failing test: Test_org_eclipse_swt_widgets_CoolItem.class, //
 		Test_org_eclipse_swt_widgets_DateTime.class, //
 		Test_org_eclipse_swt_widgets_DirectoryDialog.class, //
 		Test_org_eclipse_swt_widgets_Event.class, //
@@ -71,6 +80,7 @@
 		Test_org_eclipse_swt_widgets_ToolBar.class, //
 		Test_org_eclipse_swt_widgets_ToolItem.class, //
 		Test_org_eclipse_swt_widgets_Tree.class, //
+		Test_org_eclipse_swt_widgets_TreeColumn.class, //
 		Test_org_eclipse_swt_widgets_TreeItem.class, //
 })
 public class AllWidgetTests {

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Decorations.java

@@ -39,7 +39,7 @@
  *
  * @see org.eclipse.swt.widgets.Decorations
  */
-public class Test_org_eclipse_swt_widgets_Decorations extends Test_org_eclipse_swt_widgets_Canvas {
+public abstract class Test_org_eclipse_swt_widgets_Decorations extends Test_org_eclipse_swt_widgets_Canvas {
 
 @Override
 @Test

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Dialog.java

@@ -28,7 +28,7 @@
  *
  * @see org.eclipse.swt.widgets.Dialog
  */
-public class Test_org_eclipse_swt_widgets_Dialog {
+public abstract class Test_org_eclipse_swt_widgets_Dialog {
 
 @BeforeEach
 public void setUp() {

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Item.java

@@ -33,7 +33,7 @@
  *
  * @see org.eclipse.swt.widgets.Item
  */
-public class Test_org_eclipse_swt_widgets_Item extends Test_org_eclipse_swt_widgets_Widget {
+public abstract class Test_org_eclipse_swt_widgets_Item extends Test_org_eclipse_swt_widgets_Widget {
 
 @Override
 @Before

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Scrollable.java

@@ -22,7 +22,7 @@
  *
  * @see org.eclipse.swt.widgets.Scrollable
  */
-public class Test_org_eclipse_swt_widgets_Scrollable extends Test_org_eclipse_swt_widgets_Control {
+public abstract class Test_org_eclipse_swt_widgets_Scrollable extends Test_org_eclipse_swt_widgets_Control {
 
 @Override
 @Test