row actions and focusin focusout

[afercia]

Several kinds of listings have hidden "row actions" that are then revealed on mouse hover and on "focusin". In the specific case of comments listings, when tabbing in the Comments screen they're correctly revealed but in the Edit Post screen they don't. See screenshot:

In the Edit Post screen, comments are not ready on DOM ready :) focusin and focusout events need to be delegated.

A second issue is caused by the setTimeout used on focusout: it's needed for Firefox so it can't be removed but then Chrome doesn't remove the "visible" CSS class when there are no other focusable elements between the selected elements. This happens just in few places, for example in the Dashboard, see second screenshot where all the previous "row-actions" stay visible:

Proposed patch delegates focusin and focusout and tries to give a little help to Chrome.

[afercia]

refreshed patch after r31173

[afercia]

Refreshed patch after r31173, removes also some debugging stuff left over.

[afercia]

Patch needs a new refresh after r31177

[DrewAPicture]

Patch still needs a refresh.

[SergeyBiryukov]

Refreshed.

[SergeyBiryukov]

In 31509:

Delegate focusin and focusout events for row actions to make sure the actions are always revealed on focus.

props afercia.
fixes #29765.