Add position: relative to k-tabstrip class

[ntacheva]

Describe the bug

Related to #4624.

We've added position: relative; to the k-tabstrip-wrapper element but this is not the topmost element of the TabStrip. We should add position: relative; to the main wrapping element of the component (k-tabstrip), so that the watermark overlay does not overflow the component.

Affected package (please remove the unneeded items)

• theme-default
• theme-bootstrap
• theme-material
• theme-tasks

Affected suites (please remove the unneeded items)

• Kendo UI for jQuery
• Kendo UI for Angular
• Kendo UI for React
• Kendo UI for Vue
• Telerik UI for Blazor