fix: missing `themedContext` getter causes compilation errors (#1490)

## 📜 Description

Use getter for `themedContext` explicitly. Don't rely on auto-getters
anymore.

## 💡 Motivation and Context

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Closes
https://github.com/kirillzyusko/react-native-keyboard-controller/issues/1489

## 📢 Changelog

<!-- High level overview of important changes -->
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declarations; -->
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remove this platform/language -->

### Android

- explicitly use `getThemedContext` getter;

## 🤔 How Has This Been Tested?

Tested via CI. Old RN versions works as expected.

## 📸 Screenshots (if appropriate):

<img width="810" height="382" alt="image"
src="https://github.com/user-attachments/assets/bf2389ec-d216-473c-8989-2abff54d35cd"
/>

## 📝 Checklist

- [x] CI successfully passed
- [x] I added new mocks and corresponding unit-tests if library API was
changed