Fix double static error message

[zoecarver]

This PR changes the error message for two static patterns in a row. For example:

class Foo {
 class static func baz() { } // old: 'static' specified twice
 static class func bar() { } // new: 'class' cannot appear after another 'static' or 'class' pattern
}

Resolves SR-11265.

Not sure if I have permissions for this: @swift-ci Please test

[theblixguy]

cc @rintaro

[gregomni]

@swift-ci Please smoke test

[gregomni]

I think instead of "'static' or 'class' pattern" the message should probably be "'static' or 'class' keyword". But otherwise this is a great improvement!

[zoecarver]

Updated as per your request :)

[CodaFi]

LGTM. Will manually squash this in

@swift-ci please smoke test

[CodaFi]

Swift-CI'll get back to you soon