Fix precision issues while formatting amounts

[onyb]

User report: https://twitter.com/jim74255/status/1491103364746452994

We have no consistent way of formatting balances/amounts with rounding. Here are two most common issues we're facing with amount values:

1. very small amounts are rounded incorrectly, resulting in loss of precision.
   For example, 0.000318182 ETH will be formatted as 0.0001 ETH.
2. some amount values should never be rounded, notably anything that user will refer to before signing a transaction.
   For example, values seen in the transaction confirmation screen.
   During an internal brainstorming, we considered not rounding amounts at all, but this will result in poor UX. This issue is about bringing contextual precision to amounts by introducing better formatting tools.

[Uni-verse]

Verification Completed using:

Brave | 1.37.105 Chromium: 100.0.4896.46 (Official Build) (x86_64)
-- | --
Revision | 5ca33821b2211805855c77d334353d27c616a7ca-refs/branch-heads/4896@{#584}
OS | macOS Version 12.1 (Build 21C52)

• 6 significant figures for asset amounts
• 3 decimal places for fiat > 1 && < 10
• 1 demical places for fiat amounts > 10
• Small amounts are precise
• No unnecessary decimals for asset amounts

Txn Fee	Assets	1 < n < 10	Unnecessary decimals	precision	swap moda precision