Mechanism for displaying fields conditionally based on tags

[quincylvania]

Closes #5581.

This is a bare-bones implementation of the issue. It adds a prerequisiteTag property to the field schema that can restrict fields to show only in one of the following cases:

• A given key/value tag is present
• A given key is present with any value
• A given key is present but it does not have the given value

For example, this hides the Denomination field unless there is already a religion tag.

{
    "key": "denomination",
    "type": "combo",
    "label": "Denomination",
    "prerequisiteTag": {
        "key": "religion"
    }
}

This hides the Internet Access Fee field unless the feature has an internet_access tag not equal to no.

{
    "key": "internet_access:fee",
    "type": "check",
    "label": "Internet Access Fee",
    "prerequisiteTag": {
        "key": "internet_access",
        "valueNot": "no"
    }
}

I tried to keep it simple. If more complex conditionals are needed in the future, we can revise or build upon the design.

[mmd-osm]

For the first example, what happens to those 8000 existing pois where denomination is set, but no religion? How would you know religion is missing, if you can't see either one?

[quincylvania]

@mmd-osm Thanks for your feedback!

Fields with values are shown even if the tag prerequisite isn't met. So if there is a denomination tag, the Denomination field will appear even if there is no religion tag. If the denomination tag is removed before a religion tag is set, the Denomination field will disappear.

Also, fields defined in fields or moreFields without prerequisites will still show up. So for the School preset, the Religion fields would still appear even if empty, no matter the value of denomination or any other tag.

[bhousel]

Looks good to me, thanks @quincylvania - feel free to merge 👍