Work around ObjectSpace::WeakMap#values missing on older JRuby

JRuby before 9.3.0.0 does not define ObjectSpace::WeakMap#values
natively (jruby/jruby#6267). Patch it using JRuby's field_reader to
access the underlying Java map. Skip the patch when #values is already
defined (JRuby 9.3.0.0 or higher via jruby/jruby#6683).

Based on the approaches explored in rsim#2360 and
rsim#2413, but guards with method_defined?(:values)
instead of a version check so the workaround is skipped automatically
once JRuby provides the method natively.

Co-Authored-By: Ryudo Awaru <ryudoawaru@gmail.com>
Co-Authored-By: Thomas Steinhausen <27787+iaddict@users.noreply.github.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 4 people

lib/active_record/connection_adapters/oracle_enhanced_adapter.rb

@@ -852,7 +852,8 @@ module ActiveRecord
 end
 
 # Workaround for https://github.com/jruby/jruby/issues/6267
-if RUBY_ENGINE == "jruby"
+# Fixed in JRuby 9.3.0.0 or higher via https://github.com/jruby/jruby/pull/6683
+if RUBY_ENGINE == "jruby" && !ObjectSpace::WeakMap.method_defined?(:values)
   require "jruby"
 
   class org.jruby::RubyObjectSpace::WeakMap