Move Proc#parameters' logic to a Ruby method

Author: andrykonchin

src/main/java/org/truffleruby/core/proc/ProcNodes.java

@@ -208,11 +208,8 @@ public abstract static class ParametersNode extends PrimitiveArrayArgumentsNode
 
         @TruffleBoundary
         @Specialization
-        RubyArray parameters(RubyProc proc, Object lambdaObject) {
+        RubyArray parameters(RubyProc proc, boolean isLambda) {
             final ArgumentDescriptor[] argsDesc = proc.getArgumentDescriptors();
-            final boolean isLambda = (lambdaObject == nil)
-                    ? proc.type == ProcType.LAMBDA
-                    : !Boolean.FALSE.equals(lambdaObject);
             return ArgumentDescriptorUtils
                     .argumentDescriptorsToParameters(getLanguage(), getContext(), argsDesc, isLambda);
         }

src/main/ruby/truffleruby/core/proc.rb

@@ -130,6 +130,12 @@ def <<(other)
   end
 
   def parameters(lambda: nil)
+    if Primitive.nil?(lambda)
+      lambda = lambda?
+    else
+      lambda = Primitive.as_boolean(lambda)
+    end
+
     Primitive.proc_parameters(self, lambda)
   end
 end