Parser: allow more macros names back

[asterite]

Partially reverts #10069
Superseds #10314

This retains the "macros can't have a receiver" from #10069 but allows all kinds of names and operators for macros, including setters (this is new). Because this is perfectly fine:

class Foo
  macro bar=(x)
    puts "Setting #{ {{x}} }"
  end
end

Foo.bar = 1