let crystal tool expand find target location into the deep of require

[makenowjust]

Fixed #6098

As a side effect, crystal tool expand can expand require statement now.
I think it may help us.

Example:

$ cat -n test.cr
     1	macro test
     2	  def to_json
     3	    "hey"
     4	  end
     5	end
     6
     7	class Test
     8	  test
     9	end
$ cat -n main.cr
     1	require "./test"
     2	p Test.new.to_json
$ # issue is fixed.
$ bin/crystal tool expand -c test.cr:8:3 main.cr
1 expansion found
expansion 1:
   test

# expand macro 'test' (test.cr:1:1)
~> def to_json
     "hey"
   end

$ # now `require` can be expanded.
$ bin/crystal tool expand -c main.cr:1:1 main.cr
1 expansion found
expansion 1:
   require "./test"

~>
   # /Users/makenowjust/Projects/github.com/MakeNowJust/crystal/test.cr
   macro test
     def to_json
       "hey"
     end
   end
   class Test
     test
   end

# expand macro 'test' (/Users/makenowjust/Projects/github.com/MakeNowJust/crystal/test.cr:1:1)
~>
   # /Users/makenowjust/Projects/github.com/MakeNowJust/crystal/test.cr
   macro test
     def to_json
       "hey"
     end
   end
   class Test
     def to_json
       "hey"
     end
   end

---

Note that spec is missing for now.
Because there are no foundation to write tool expand spec over multiple files currently.
How to write spec is better...?