Correct forwarded refs

[martimalek]

What:

Make refs point to the most obvious element in Input and Password components and correct refs usages in our components. Apart from that I've also removed the forwardRef from our internal Datepicker component since it wasn't being used (this is not a component exposed by Wave, it's used internally by DatepickerSingleInput and DatepickerRangeInput)

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Why:

To correct our usages of refs so that it follows our agreement.

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How:

• Correct ref type in Input, Password and InnerInput to HTMLInputElement
• Correct the ref in InnerInput so it's passed to the input instead of to the wrapper
• Adapt DatepickerRangeInput to use the new Input ref
• Adapt PhoneInput to use the new Input ref
• Remove forwardRef from Datepicker

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Other:

After this PR we are only forwarding refs in 3 places in the codebase:

• Input and Password components (external components that our users can use)
• InnerInput component (internal component that we don't expose, needed for Input and Password)

Since the ref in the Datepicker (internal) was not being used in either of it's parents (the actual Datepicker and DatepickerRangeInput components that we expose) there was no way for a project to depend on this ref, so I've decided to remove it. Even if in the future we decide to have a ref/refs in Datepicker it will point to a different element, since the one removed did not follow our agreement on refs.

Checklist:

• Check ref in internal Datepicker
• Ready to be merged

Closes #169