swift234

Validate @IBAction method signatures.

// IBAction, OS X:
@IBAction func foo(sender: AnyObjCClassCompatibleType?)

// IBAction, iOS:
@IBAction func foo()
@IBAction func foo(sender: AnyObjCClassCompatibleType?)
@IBAction func foo(sender: AnyObjCClassCompatibleType?, event: UIEvent?)

All argument types may be unchecked-optional or non-optional as well.
This commit doesn't check that the second argument to an iOS action method
is a UIEvent; the user may want to declare it as AnyObject or perhaps some
other protocol, so I just left it unenforced.

I'm also drawing on my knowledge of Cocoa to disallow String as an IBAction
parameter. Array and Dictionary also shouldn't appear here and thus don't
need special-casing even when bridged.

Finishes up <rdar://problem/16281474>

Swift SVN r17049