menu: should close when pressing tab

[jelbourn]

Currently, when you tab from an open menu it moves through the items and then escapes the panel into the rest of the page. The menu should actually just close upon pressing tab and the focus should move to the next focusable element (the menu items shouldn't be tab stops). MatMenu does the right thing for this and can be an example.

[Splaktar]

I've created a simple CodePen that demonstrates the issue.

[Splaktar]

Also the examples for menuBar in the docs have the same problem. Just to confirm, this change would not disable keyboard interaction with the menus (which can still be done with the arrow keys). It would just close the menu on TAB in addition to ESCAPE.

[Splaktar]

PR is posted.

[jelbourn]

Yes, and tab should also still advance to the next element in the tab order.