Add utilities for formatting token amounts (`formatTokenAmount` and `parseTokenAmount`)

[jeesunikim]

Summary:

• adding soroban token display formatter and parser from
• moving the commonly used functions parseTokenAmount and formatTokenAmount from soroban-react-payment

[Shaptic]

I'm confused about why CI isn't running :raised_eyebrow:

[aristidesstaffieri]

btw the original inspiration for these is here and they do some extra stuff that we don't like work with negative values so maybe worth discussing? Ours have worked for all of our use cases so far but they may get used differently as part of the sdk.

[Shaptic]

@aristidesstaffieri thanks for the ref! we should steal their (non-negative) test cases, then. I think the usage aligns (besides multiplier, which I don't understand).

Btw, a lot of the code comments in this review I'd make there, too, but I bet theirs was written before e.g. .padEnd or ?? support was common in JS.

[aristidesstaffieri]

I'm confused about why CI isn't running 🤨

Github is having issues, probably related https://www.githubstatus.com/incidents/nwb8m3ppfxw6

[github-actions[bot]]

Size Change: +50.6 kB (+2%)

Total Size: 3.13 MB

Filename	Size	Change
dist/stellar-base.js	2.3 MB	+36.8 kB (+2%)
dist/stellar-base.min.js	834 kB	+13.7 kB (+2%)

_{compressed-size-action}