Adjust 'Type Aliases' to outlaw explicit type arguments in static method call

[eernstg]

The current text in the section 'Type Aliases' in the language specification implies that it is possible to invoke a static method staticMethod of a class C via a type alias F with type arguments:

class C<X> {
  void staticMethod() {}
}
typedef F<X> = C<X>;

void main() {
  F<int>.staticMethod();
}

This should be an error, and the tests expect that it is an error, but the spec language said otherwise. This PR changes the spec text to follow the intention and tests, and makes it an error to include type arguments in this kind of static method invocation.

It also changes the grammar such that a type alias can denote a <type> rather than just a <functionType>, hence "enabling" non-function type aliases in general.