1:1 mapping of require/provide in Dojo Core

[dante]

refs #8017 - along the lines of stub loader files for Dijit, we should try to follow the same patterns in Dojo (required?) and DojoX (best practice, but not always feasible).

Propose moving dojo.fx.!Toggler out of dojo/fx.js and into dojo/fx/Toggler.js, and putting a require for toggler in fx.js to preserve backwards compatibility until 2.0

dojo.Color is an offender, too, but is defined in base and does not carry such a straightforward solution.

[dante]

(In [16190]) fixes #8317 - moving Toggler out into own file for 1:1 mapping and size considerations (though a require() is issued in fx.js for backward compatibility, it may be wrapped in a deprecated build tag as per #8271) !strict