Use SQL literals for column_definitions and pk_and_sequence_for

since these methods called via `to_sql` method under `unprepared_statement`

Fix rsim#1678

Starting from Oracle enhanced adapter 5.2.0.beta1 most of the queries for the dictionary, such as all_sequences use bind variables by rsim#1498 .
It should help shared memory usage however, which eventually means Oracle enhanced adapter 5.2+ only supports `prepared_statements: true`
as Rails default configuration but it does not support `prepared_statements: false`.

Even if `prepared_statements: true`, `to_sql` uses `unprepared_statement` to generate SQL statement. If the connection already knows which table is associated with which model object in advance, `to_sql` works fine but when `to_sql` executed first the connection needs to know these relation then call
column_definitions` and `pk_and_sequence_for` methods at least.

Author: yahonda

lib/active_record/connection_adapters/oracle_enhanced_adapter.rb

@@ -525,9 +525,9 @@ def default_tablespace
       end
 
       def column_definitions(table_name)
-        (_owner, desc_table_name) = @connection.describe(table_name)
+        (owner, desc_table_name) = @connection.describe(table_name)
 
-        select_all(<<-SQL.strip.gsub(/\s+/, " "), "Column definitions", [bind_string("table_name", desc_table_name)])
+        select_all(<<-SQL.strip.gsub(/\s+/, " "), "Column definitions")
           SELECT cols.column_name AS name, cols.data_type AS sql_type,
                  cols.data_default, cols.nullable, cols.virtual_column, cols.hidden_column,
                  cols.data_type_owner AS sql_type_owner,
@@ -540,8 +540,8 @@ def column_definitions(table_name)
                  DECODE(data_type, 'NUMBER', data_scale, NULL) AS scale,
                  comments.comments as column_comment
             FROM all_tab_cols cols, all_col_comments comments
-           WHERE cols.owner      = SYS_CONTEXT('userenv', 'current_schema')
-             AND cols.table_name = :table_name
+           WHERE cols.owner      = '#{owner}'
+             AND cols.table_name = #{quote(desc_table_name)}
              AND cols.hidden_column = 'NO'
              AND cols.owner = comments.owner
              AND cols.table_name = comments.table_name
@@ -553,21 +553,21 @@ def column_definitions(table_name)
       # Find a table's primary key and sequence.
       # *Note*: Only primary key is implemented - sequence will be nil.
       def pk_and_sequence_for(table_name, owner = nil, desc_table_name = nil) #:nodoc:
-        (_owner, desc_table_name) = @connection.describe(table_name)
+        (owner, desc_table_name) = @connection.describe(table_name)
 
-        seqs = select_values(<<-SQL.strip.gsub(/\s+/, " "), "Sequence", [bind_string("sequence_name", default_sequence_name(desc_table_name).upcase)])
+        seqs = select_values(<<-SQL.strip.gsub(/\s+/, " "), "Sequence")
           select us.sequence_name
           from all_sequences us
-          where us.sequence_owner = SYS_CONTEXT('userenv', 'current_schema')
-          and us.sequence_name = :sequence_name
+          where us.sequence_owner = '#{owner}'
+          and us.sequence_name = upper(#{quote(default_sequence_name(desc_table_name))})
         SQL
 
         # changed back from user_constraints to all_constraints for consistency
-        pks = select_values(<<-SQL.strip.gsub(/\s+/, " "), "Primary Key", [bind_string("table_name", desc_table_name)])
+        pks = select_values(<<-SQL.strip.gsub(/\s+/, " "), "Primary Key")
           SELECT cc.column_name
             FROM all_constraints c, all_cons_columns cc
-           WHERE c.owner = SYS_CONTEXT('userenv', 'current_schema')
-             AND c.table_name = :table_name
+           WHERE c.owner = '#{owner}'
+             AND c.table_name = #{quote(desc_table_name)}
              AND c.constraint_type = 'P'
              AND cc.owner = c.owner
              AND cc.constraint_name = c.constraint_name

spec/active_record/connection_adapters/oracle_enhanced_adapter_spec.rb

@@ -480,15 +480,15 @@ class ::TestPost < ActiveRecord::Base
       expect(@conn.table_exists?("NOT_EXISTING")).to eq false
     end
 
-    it "should return content from columns with bind usage" do
+    it "should return content from columns without bind usage" do
       expect(@conn.columns("TEST_POSTS").length).to be > 0
-      expect(@logger.logged(:debug).last).to match(/:table_name/)
-      expect(@logger.logged(:debug).last).to match(/\["table_name", "TEST_POSTS"\]/)
+      expect(@logger.logged(:debug).last).not_to match(/:table_name/)
+      expect(@logger.logged(:debug).last).not_to match(/\["table_name", "TEST_POSTS"\]/)
     end
 
-    it "should return pk and sequence from pk_and_sequence_for with bind usage" do
+    it "should return pk and sequence from pk_and_sequence_for without bind usage" do
       expect(@conn.pk_and_sequence_for("TEST_POSTS").length).to eq 2
-      expect(@logger.logged(:debug).last).to match(/\["table_name", "TEST_POSTS"\]/)
+      expect(@logger.logged(:debug).last).not_to match(/\["table_name", "TEST_POSTS"\]/)
     end
 
     it "should return pk from primary_keys with bind usage" do