Add two new APIs for active keyboard layout.

This goes with https://github.com/adobe/brackets/pull/9652.
Wouldn't it be better to call `GetKeyboardLayoutName()` instead?  You get a string back, you don't have to fiddle with a language id or anything.  It would return, for U.S. English, "00000409". Variants of U.S. English layout (such as the Dvorak layout) are named "00010409", "00020409", and so on.  This sounds like the data you're looking to return back to the JS layer