Media library arrow key navigation is triggered in textareas

[essha]

This is a follow-up to #28704.
Event is fired on arrow keys when you enter textarea, i.e. caption and description.
Please exlude TEXTAREA from event trigger as well.
https://core.trac.wordpress.org/attachment/ticket/28704/28704.diff

[ryelle]

Ran into this problem last night- the keyEvent function returns when the event target is an input, but not on textareas, so editing the captions becomes very frustrating (since the attachment changes out from under you).

29725.diff​ adds textarea to the conditional, and also switches to nodeName based on azaozz's comment on r29332.

[ocean90]

#29776 was marked as a duplicate.

[wonderboymusic]

In 29777:

Media Grid: when the modal is open, don't respond to arrow keys when <textarea> has focus.

Props ryelle.
Fixes #29725.

[jorbin]

I verified that r29777 applies correctly to the 4.0 branch and fixes the described issue. Tested in chrome 38 and 40 along with FF.

This is ready to be merged.

[johnbillion]

In 30378:

Update the inline docs for the keyEvent callback in the media grid.

Props adamsilverstein
See #29725

[adamsilverstein]

#30400 was marked as a duplicate.

[nacin]

In 30407:

Media Grid: when the modal is open, don't respond to arrow keys when <textarea> has focus.

Merges [29777] (and [30378]) to the 4.0 branch.

Props ryelle, adamsilverstein.
Fixes #29725.