Support generic types in Crystal::Macros::Type#is_a?

[HertzDevil]

Resolves #11981. With this, all the type names used in the macro method docs will actually mean something (even if they aren't used yet).

This PR makes the following macro types generic:

class ArrayLiteral(T); end      # T = union of element types
class HashLiteral(K, V); end    # K = union of key types, V = union of value types
class TupleLiteral(T); end      # T = union of element types
class NamedTupleLiteral(V); end # V = union of value types

But see #11981 (comment) on whether the last two should become variadic.

The second commit forbids all of the short forms that are previously allowed in arguments to the macro #is_a?. As mentioned in #11981, they never worked in the first place, because no AST node's #class_name ever contains those short forms or the type names they expand to:

x = 1
x.is_a?(NumberLiteral?)   # => false
nil.is_a?(NumberLiteral?) # => false

# after #12086
x = 1
x.is_a?(NumberLiteral?)   # => true
nil.is_a?(NumberLiteral?) # => false

# after this PR
x = 1
x.is_a?(NumberLiteral?)   # Error: cannot use `?` in macro types
nil.is_a?(NumberLiteral?) # Error: cannot use `?` in macro types

A corresponding PR for the reference manual will follow shortly.