deprecated.json: allow more strict matching rules for values of semicolon-separated tags

[tyrasd]

Sometimes, upgrade paths need to handle semicolon-separated tags differently depending if only a single value is present or a combination of multiple values. For example consider the following situation:

• old_tag=a ➡️ new_tag=x + new_sub_tag=a
• old_tag=b ➡️ new_tag=x + new_sub_tag=b
• old_tag=a;b ➡️ new_tag=x

Such a tagging upgrade is currently (in general) not possible to implement using the deprecated.json and/or preset replacement mechanisms. The first because multiple upgrade paths will match the a;b value, causing the new_sub_tag to be incorrectly added in the result. The preset replacement mechanism does not work if there is only a single preset for new_tag=x (and a field for new_sub_tag).

See openstreetmap/id-tagging-schema#365 (comment) for a case where such a bug occurred.

One solution would be to allow the matching of old tags to be more strict, e.g. by being able to indicate that semicolon-separated values should not be considered. Possible syntax:

  {
    "old": {"old_tag": "a"},
    "matchSemicolonSeparatedValues": false,
    "replace": {"new_tag": "x", "new_sub_tag": "a"}
  },

The property could also be called "match": "exact" to be a bit more concise.

The downside of this approach would be that it would not be backwards compatible with older versions of iD (once it is implemented). 🤔