IR: minor, improve toString for IrBasedTypeParameterDescriptor

The motivation is that in the "Unbound symbols are not allowed" error
message like the one in KT-46069, the type parameter is rendered via
`render()`, and that contains only its name/variance, and doesn't help
in finding where the member with that type parameter is declared.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/IrBasedDescriptors.kt

@@ -304,6 +304,7 @@ open class IrBasedTypeParameterDescriptor(owner: IrTypeParameter) : TypeParamete
         visitor!!.visitTypeParameterDescriptor(this, null)
     }
 
+    override fun toString(): String = super.toString() + "\nParent: $containingDeclaration"
 }
 
 fun IrTypeParameter.toIrBasedDescriptor() = IrBasedTypeParameterDescriptor(this)