[ruby/fiddle] Move "type" constants to Fiddle::Types (https://github.com/ruby/fiddle/pull/112)

This helps to reduce repetition in code. Instead of doing "TYPE_*"
everywhere, you can do `include Fiddle::Types`, and write the type name
directly.

This PR is to help reduce repetition when writing Fiddle code. Right now
we have to type `TYPE_` everywhere, and you also have to include all of
`Fiddle` to access `TYPE_*` constants. With this change, you can just
include `Fiddle::Types` and it will shorten your code and also you only
have to include those constants.

Here is an example before:

```ruby
require "fiddle"

module MMAP
  # All Fiddle constants included
  include Fiddle

  def self.make_function name, args, ret
    ptr = Handle::DEFAULT[name]
    func = Function.new ptr, args, ret, name: name
    define_singleton_method name, &func.to_proc
  end

  make_function "munmap", [TYPE_VOIDP, # addr
                           TYPE_SIZE_T], # len
                           TYPE_INT

  make_function "mmap", [TYPE_VOIDP,
                         TYPE_SIZE_T,
                         TYPE_INT,
                         TYPE_INT,
                         TYPE_INT,
                         TYPE_INT], TYPE_VOIDP

  make_function "mprotect", [TYPE_VOIDP, TYPE_SIZE_T, TYPE_INT], TYPE_INT
end
```

After:

```ruby
require "fiddle"

module MMAP
  # Only type names included
  include Fiddle::Types

  def self.make_function name, args, ret
    ptr = Fiddle::Handle::DEFAULT[name]
    func = Fiddle::Function.new ptr, args, ret, name: name
    define_singleton_method name, &func.to_proc
  end

  make_function "munmap", [VOIDP, # addr
                           SIZE_T], # len
                           INT

  make_function "mmap", [VOIDP, SIZE_T, INT, INT, INT, INT], VOIDP

  make_function "mprotect", [VOIDP, SIZE_T, INT], INT
end
```

We only need to import the type names, and you don't have to type
`TYPE_` over and over. I think this makes Fiddle code easier to read.

49fa7233e5

Co-authored-by: Sutou Kouhei <kou@clear-code.com>

ext/fiddle/lib/fiddle.rb

@@ -67,4 +67,8 @@ module Fiddle
   RTLD_GLOBAL = Handle::RTLD_GLOBAL # :nodoc:
   RTLD_LAZY   = Handle::RTLD_LAZY   # :nodoc:
   RTLD_NOW    = Handle::RTLD_NOW    # :nodoc:
+
+  Fiddle::Types.constants.each do |type|
+    const_set "TYPE_#{type}", Fiddle::Types.const_get(type)
+  end
 end