Let's move the constants that describe the keys in the valueInfo map that a typed variable value has to a public package (e.g. the constants here: https://github.com/camunda/camunda-commons/blob/master/typed-values/src/main/java/org/camunda/bpm/engine/impl/core/variable/type/FileValueTypeImpl.java).
- it is practically API since the map with values is public API
- the value info concept exists for almost a year now and we haven't had issues with this (I think this was a reason we hesistated making the keys public API at that time)
- using these constants in the REST API becomes more robust