Redo MoneyInput (better UX, less error cases)

[dferber90]

The old MoneyInput was capable of displaying an error either on the currency dropdown or the amount input:

hasCurrencyError	hasAmountError

After talking to @filippobocik we agreed to drop the individual error states from MoneyInput. MoneyInput will now only accept hasError (and hasWarning) instead of hasCurrencyError and hasAmountError.

<MoneyInput
- hasAmountError={true}
- hasCurrencyError={true}
- hasAmountWarning={true}
- hasCurrencyWarning={true}
+ hasError={true}
+ hasWarning={true}
/>

This makes the code easier for consumers as they only need to worry about one error state and they don't need to worry about individual touched states anymore to display the errors in the right cases.

Old MoneyInput in a form

• Notice how the error appears while the user is still interacting with the MoneyInput. It pops up before the user has a chance to type the amount.

New MoneyInput in a form

• The error only appears when the user leaves the MoneyInput completely
• The amount-input gets focused automatically after selecting a currency to improve UX

Play with it https://deploy-preview-175--mc-uikit.netlify.com/?selectedKind=Examples%7CForms%2FInputs&selectedStory=MoneyInput&full=0&addons=1&stories=1&panelRight=1&addonPanel=storybook%2Factions%2Factions-panel.

[dferber90]

Tests are failing. I'll rewrite them with react-testing-library and ping ya'll again once it's ready for dev review. UX review can continue.

[dferber90]

Note to self: MoneyField supports errors.missing, as do all fields. But there is a difference between a missing value and an incomplete value. A missing-value-error only happens for required fields, while a incomplete-value-error can happen for optional fields (e.g. when an amount is provided, but no currency).

We should add errors.incomplete to MoneyField and handle that. Maybe also MoneyField.isIncomplete to determine such cases.

[dferber90]

New tests with react-testing-library are up!

I skipped converting the tests related to styling as testing classnames doesn't seem like the right way for this anyways.

[tdeekens]

The UX simplification is real nice. Maybe there is one mistake in the docs. Not sure.