Allow adding / editing addr:unit together with housenumber

[Helium314]

Use case

• more detailed address information
• avoids duplication of unit information, e.g. when a user uses address overlay to add already tagged unit number into housenumber (because in SC, unit is not displayed)

Proposed Solution
There could be a unit field next to the house number field.
Maybe auto-hidden and only shown after selecting some uh... answer (similar to house name), and showing automatically when a unit number is expected for some reason.
There are some more things to consider regarding addr:block and addr:flats, see Helium314#897 (comment)

[westnordost]

Currently when selecting "it's within a city block", the block number is specified in the same line as the housenumber. As a house number could theoretically be within a city block and also be further split up into units, I think the block number would need to always be in its own line. I.e.

[ city block ]
[ house number ] [ unit number ]

(or even, just put everything each in its own line)

[Helium314]

Each in a separate line might get a bit high, since the input field is rather large. But sometimes it will be necessary even for 2 fields.
Maybe use a FlowRow so people with wide enough screens still can have mulitple inputs in a row?