Require blank lines between methods

[MidnightDesign]

This makes the following code invalid:

interface NoEmptyLineBetweenInterfaceMethods
{
    public function methodA(): void;
    public function methodB(): void;
}

This is valid:

interface SingleBlankLineBetweenInterfaceMethods
{
    public function methodA(): void;

    public function methodB(): void;
}