Cannot call focus on tab bar

[steverep]

Describe the bug The mwc-tab-bar component cannot be focused programmatically via focus method. For example, if a tab bar is desired to gain focus inside a dialog, focusing the active tab by calling focus on the tab bar element is not possible.

To Reproduce Steps to reproduce the behavior:

1. Try to call focus on mwc-tab-bar and nothing happens
2. See error

Expected behavior Focus should be placed on the active tab.

Browser Version (please complete the following information):

• OS: Windows 10
• Browser Firefox or Chrome
• Version latest

Additional context ARIA Authoring Practices on Tabs