Move RelativePositioning.range to correct file

This fixes autoload problems where we get NoMethodError when
lib/gitlab/relative_positioning/range.rb is not loaded yet.

lib/gitlab/relative_positioning.rb

@@ -13,5 +13,18 @@ module Gitlab
     MIN_GAP = 2
 
     NoSpaceLeft = Class.new(StandardError)
+    IllegalRange = Class.new(ArgumentError)
+
+    def self.range(lhs, rhs)
+      if lhs && rhs
+        ClosedRange.new(lhs, rhs)
+      elsif lhs
+        StartingFrom.new(lhs)
+      elsif rhs
+        EndingAt.new(rhs)
+      else
+        raise IllegalRange, 'One of rhs or lhs must be provided' unless lhs && rhs
+      end
+    end
   end
 end

lib/gitlab/relative_positioning/range.rb

@@ -2,8 +2,6 @@
 
 module Gitlab
   module RelativePositioning
-    IllegalRange = Class.new(ArgumentError)
-
     class Range
       attr_reader :lhs, :rhs
 
@@ -34,18 +32,6 @@ module Gitlab
       end
     end
 
-    def self.range(lhs, rhs)
-      if lhs && rhs
-        ClosedRange.new(lhs, rhs)
-      elsif lhs
-        StartingFrom.new(lhs)
-      elsif rhs
-        EndingAt.new(rhs)
-      else
-        raise IllegalRange, 'One of rhs or lhs must be provided' unless lhs && rhs
-      end
-    end
-
     class ClosedRange < RelativePositioning::Range
       def initialize(lhs, rhs)
         @lhs, @rhs = lhs, rhs