Checking for the 'wp' JavaScript variable could be simpler

[evansolomon]

In a few places we do this:

if ( typeof wp === 'undefined' )
    var wp = {};

That could be simplified to a one liner that's easier to read:

window.wp = window.wp || {};

Nice patch.

In [22126]:

Improve the lazy instantiation of the 'wp' JavaScript variable. props evansolomon, fixes #22113.