Reflection: add KTypeParameter.toString

The test covers different type parameters with and without bounds, in case we
decide to also output upper bounds in toString

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KTypeParameterImpl.kt

@@ -45,4 +45,7 @@ internal class KTypeParameterImpl(override val descriptor: TypeParameterDescript
 
     override fun hashCode() =
             descriptor.hashCode()
+
+    override fun toString() =
+            ReflectionObjectRenderer.renderTypeParameter(descriptor)
 }

core/reflection.jvm/src/kotlin/reflect/jvm/internal/ReflectionObjectRenderer.kt

@@ -16,12 +16,10 @@
 
 package kotlin.reflect.jvm.internal
 
-import org.jetbrains.kotlin.descriptors.CallableDescriptor
-import org.jetbrains.kotlin.descriptors.FunctionDescriptor
-import org.jetbrains.kotlin.descriptors.PropertyDescriptor
-import org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor
+import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.renderer.DescriptorRenderer
 import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.Variance
 import kotlin.reflect.KParameter
 
 internal object ReflectionObjectRenderer {
@@ -107,6 +105,18 @@ internal object ReflectionObjectRenderer {
         }
     }
 
+    fun renderTypeParameter(typeParameter: TypeParameterDescriptor): String {
+        return buildString {
+            when (typeParameter.variance) {
+                Variance.INVARIANT -> {}
+                Variance.IN_VARIANCE -> append("in ")
+                Variance.OUT_VARIANCE -> append("out ")
+            }
+
+            append(typeParameter.name)
+        }
+    }
+
     fun renderType(type: KotlinType): String {
         return renderer.renderType(type)
     }