docs: better lottie animations (#200)

## 📜 Description

Re-worked `cross-platform` and `interactive` lottie animations 🎞 🎥 

## 💡 Motivation and Context

To make main page more attractive I've decided to slightly improve
animations. Now they are all dynamic + they are synchronized with each
other (time of opening keyboard) which makes it easy for visual
perception 😊

## 📢 Changelog

### Docs
- crossplatform animation is now dynamic (i. e. it's not just an image
and it makes it more attractive);
- interactive animation duration now is 3s -> it's synchronized with
other animations;

## 🤔 How Has This Been Tested?

Tested on localhost:3000 + preview.

## 📝 Checklist

- [x] CI successfully passed