Fix parameter binding issue.

Introduce a new `bind_block` method. Mimicking this change in the
postgres adapter: rails/rails@2b35775

Provides the expected :aN formatted bind parameter values needed by
oci8.

Thanks to dlaggero for this.
#2424 (comment)

Author: andynu

lib/arel/visitors/oracle.rb

@@ -195,14 +195,6 @@ def split_order_string(string)
           array
         end
 
-        def visit_ActiveModel_Attribute(o, collector)
-          collector.add_bind(o) { |i| ":a#{i}" }
-        end
-
-        def visit_Arel_Nodes_BindParam(o, collector)
-          collector.add_bind(o.value) { |i| ":a#{i}" }
-        end
-
         def is_distinct_from(o, collector)
           collector << "DECODE("
           collector = visit [o.left, o.right, 0, 1], collector

lib/arel/visitors/oracle12.rb

@@ -100,14 +100,6 @@ def visit_Arel_Nodes_UpdateStatement(o, collector)
           super
         end
 
-        def visit_ActiveModel_Attribute(o, collector)
-          collector.add_bind(o) { |i| ":a#{i}" }
-        end
-
-        def visit_Arel_Nodes_BindParam(o, collector)
-          collector.add_bind(o.value) { |i| ":a#{i}" }
-        end
-
         def is_distinct_from(o, collector)
           collector << "DECODE("
           collector = visit [o.left, o.right, 0, 1], collector

lib/arel/visitors/oracle_common.rb

@@ -3,6 +3,12 @@
 module Arel # :nodoc: all
   module Visitors
     module OracleCommon
+
+      BIND_BLOCK = proc { |i| ":a#{i}" }
+      private_constant :BIND_BLOCK
+
+      def bind_block; BIND_BLOCK; end
+
       private
         # Oracle can't compare CLOB columns with standard SQL operators for comparison.
         # We need to replace standard equality for text/binary columns to use DBMS_LOB.COMPARE function.