Define Crystal::Macros::Path#global? properly

[HertzDevil]

The API docs mention Crystal::Macros::Path#global?, but it was actually #global that was defined:

macro foo(node)
  {% p node.global %}
end

macro bar(node)
  {% p node.global? %}
end

foo(Int32)   # => false
foo(::Int32) # => true
bar(Int32)   # Error: undefined macro method 'Path#global?'
bar(::Int32) # Error: undefined macro method 'Path#global?'

This PR adds #global? back. It makes sense that this is a question method since it is a predicate returning a BoolLiteral. To maintain compatibility, the old #global is now marked as deprecated using the facilities introduced in #9950.