fixes separators logic disparities

[EvgeniiaVak]

fixes #191

• Removes disparities between separator logic for different components.
• Removes the separators params from displayAmount function - we don't want users to ever pass something non-standard here (something that is different than the rest of the page). They are not needed for tests, because just mock setup ensures consistent separators.
• Ensures there is always a thousand separator (because it simplifies code and on macs for some reason even when selecting a number format with spaces - the browser thinks there is no thousands separator, "").

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