Sui TypeScript SDK: Add formatAmount() util

[kkomelin]

Problem/Motivation

It would be good to have a standard way to format Sui amounts with TypeScript SDK, like existing formatDigest() or formatAddress().
It's a very trivial operation and it's necessary for many projects, so it deserves to be standardised, in my opinion.

And, moreover, you already have it implemented here: formatAmount()

Look how even example projects now have to copy&paste the code. Not the best way because you cannot pull the latest bug fixes and updates automatically.

Proposed resolution

Move formatAmount() function from apps to TypeScript SDK utils.