Fix incorrect node usage in ImmutableClassNode#execute

* This would cause `this` to be a global singleton unadopted node and
  behave the same as RubyContext.get(null), which does not fold to a
  constant with a single context but reads it from the fast thread local.

Author: eregon

src/main/java/org/truffleruby/language/objects/ImmutableClassNode.java

@@ -12,6 +12,7 @@
 import com.oracle.truffle.api.dsl.GenerateCached;
 import com.oracle.truffle.api.dsl.GenerateInline;
 import com.oracle.truffle.api.nodes.Node;
+import org.truffleruby.RubyContext;
 import org.truffleruby.core.CoreLibrary;
 import org.truffleruby.core.encoding.RubyEncoding;
 import org.truffleruby.core.klass.RubyClass;
@@ -36,7 +37,7 @@
 public abstract class ImmutableClassNode extends RubyBaseNode {
 
     public final RubyClass execute(Node node, Object value) {
-        return execute(node, value, coreLibrary());
+        return execute(node, value, RubyContext.get(node).getCoreLibrary());
     }
 
     protected abstract RubyClass execute(Node node, Object value, CoreLibrary coreLibrary);

test/truffle/compiler/pe/core/class_pe.rb

@@ -12,6 +12,14 @@ module ClassPEFixtures
   AInstance = ClassPEFixtures::A.new
 end
 
+example "1.class", Integer
+example "1.2.class", Float
+example "true.class", TrueClass
+example "nil.class", NilClass
+example "/regexp/.class", Regexp
+example "(1..2).class", Range
+example ":symbol.class", Symbol
+
 example "ClassPEFixtures::B.superclass", ClassPEFixtures::A
 example "ClassPEFixtures::A.new.class", ClassPEFixtures::A