TextInput promptTextRenderer has no stateContext added

[divlaine]

There are some theme cases when we need to change prompt fontStyle in different TextInput states. promptTextRenderer has neccesary support, but after statechange no change. After some searching I found that there is no stateContext added to it.
So my propose is to add in createPrompt function
IStateObserver(this.promptTextRenderer).stateContext = this;