[yahonda]

Depends on #2941. This branch is stacked on it, so the first two commits belong to #2941; please review the last three commits (a738cfc, fd704bd and 101ee0c) here.

The Oracle Arel visitor now renders a non-empty returning on INSERT, UPDATE and DELETE statements as Oracle's RETURNING <columns> INTO <placeholders>, adding an OUT bind for each column with its type from the schema cache. The adapter already reads OUT binds back after execution, so Active Record's own apply_returning_to! and update_with_result work unchanged.

Changes

• OracleCommon#visit_Arel_Nodes_{Insert,Update,Delete}Statement render returning as RETURNING ... INTO. A node that is not a column of the target table, such as Arel.star or a column of another table, raises ArgumentError, as does a column whose type cannot be read back through an OUT bind, such as DATE.
• apply_returning_to! delegates Arel INSERTs to Active Record and keeps the string append only for SQL strings.
• Without prepared statements, SubstituteBinds would inline the OUT binds as NULL, so to_sql_and_binds keeps every bind as a placeholder for statements with returning.

Removed

• The update_with_result override from Refresh virtual columns on update with RETURNING ... INTO #2941 and the query cache dirtying wrapper it needed.
• The ArgumentError for Arel returning added in Raise for Arel statements with returning #2936.

Direct Arel callers can now use returning, which is option (a) in #2796:

t = Arel::Table.new(name: :items)
dm = Arel::DeleteManager.new.from(t).where(t[:id].eq(1)).returning([t[:id], t[:name]])
ActiveRecord::Base.lease_connection.to_sql(dm)
# => DELETE FROM "ITEMS" WHERE "ITEMS"."ID" = 1 RETURNING "ITEMS"."ID", "ITEMS"."NAME" INTO :a1, :a2

The specs run INSERT, UPDATE and DELETE statements like this with and without prepared statements and read the returned rows.

INSERT statements built by Active Record now use the visitor's placeholders (:aN) instead of :returning_<column>.

Tests

Full suite against rails/rails@2fe713e2e0:

	prepared statements	ORACLE_ENHANCED_PREPARED_STATEMENTS_FALSE=1
CRuby (OCI)	1216 examples, 0 failures	1216 examples, 0 failures
JRuby	1223 examples, 0 failures	1223 examples, 0 failures