[ISSUE#1881][MAS2.1.2][Keyboard Navigation- Welcome Tab screen] Focus gets trapped on first and last element of the page when user navigates through the page

[denscollo]

Solves #1881

Description

Fixes how the focus gets trapped between the last and the first element of the pane.

Changes made

We added a new condition to the EventHandlers class which will manage the focus when the emulator is running in macOS. Also, we included two auxiliary methods to find the first and last elements of the active pane and be able to move the focus between them.

Additionally, we added two unit tests to cover the new keydown event.

Testing

In the following image, you can see how the focus goes from the last element of the pane to the first when navigating with Tab key and vice-versa when using Shift+Tab navigation:

[coveralls]

Coverage increased (+0.08%) to 68.75% when pulling 50b4d5c on fix/focus-trap-in-mac-navigation into cb08d7d on master.

[corinagum]

Thanks for the help! Just a couple of small changes.

[denscollo]

@corinagum if we move lines 142 & 143 to the ones that you told us, the isFirstElement and isLastElement variables are not going to work. If you want us to move those line, we need to update the if clause to be something like:
if (shiftPressed && document.activeElement === document.querySelector('nav').firstElementChild as HTMLElement) { }

And something similar would happen to the other if clause, since it uses lastDecendants to obtain the lastElement.

Let us know if you want us to proceed with this change.