Fix incorrect position of column selector in MPR (#11946)

* Change ContextMenu position from absolute to fixed

* Use getBoundingClientRect to get the coordinates of columnSelector in
VScrollTable when the context menu is being opened

* Update TableTooManyColumnsTest screenshot

* Upgrade Chrome version in VerifyBrowserVersionTest

* Update ValoThemeUITest-sliders screenshot

client/src/main/java/com/vaadin/client/ui/VContextMenu.java

@@ -20,6 +20,7 @@ import com.google.gwt.core.client.Scheduler;
 import com.google.gwt.core.client.Scheduler.ScheduledCommand;
 import com.google.gwt.dom.client.Element;
 import com.google.gwt.dom.client.NodeList;
+import com.google.gwt.dom.client.Style;
 import com.google.gwt.dom.client.TableRowElement;
 import com.google.gwt.dom.client.TableSectionElement;
 import com.google.gwt.event.dom.client.BlurEvent;
@@ -166,6 +167,7 @@ public class VContextMenu extends VOverlay implements SubPartAware {
                     setHeight(Window.getClientHeight() + "px");
                 }
                 setPopupPosition(left, top);
+                getElement().getStyle().setPosition(Style.Position.FIXED);
 
                 /*
                  * Move keyboard focus to menu, deferring the focus setting so

client/src/main/java/com/vaadin/client/ui/VScrollTable.java

@@ -3926,10 +3926,12 @@ public class VScrollTable extends FlowPanel
         public void onBrowserEvent(Event event) {
             if (enabled) {
                 if (event.getEventTarget().cast() == columnSelector) {
-                    final int left = DOM.getAbsoluteLeft(columnSelector);
-                    final int top = DOM.getAbsoluteTop(columnSelector)
+                    WidgetUtil.TextRectangle clientRect = WidgetUtil
+                            .getBoundingClientRect(columnSelector);
+                    final int left = (int) clientRect.getLeft();
+                    final int top = (int) (clientRect.getTop()
                             + DOM.getElementPropertyInt(columnSelector,
-                                    "offsetHeight");
+                                    "offsetHeight"));
                     client.getContextMenu().showAt(this, left, top);
                 }
             }

uitest/src/test/java/com/vaadin/tests/VerifyBrowserVersionTest.java

@@ -25,7 +25,7 @@ public class VerifyBrowserVersionTest extends MultiBrowserTest {
             // Chrome version does not necessarily match the desired version
             // because of auto updates...
             browserIdentifier = getExpectedUserAgentString(
-                    getDesiredCapabilities()) + "78";
+                    getDesiredCapabilities()) + "81";
         } else {
             browserIdentifier = getExpectedUserAgentString(desiredCapabilities)
                     + desiredCapabilities.getVersion();