Add EnumeratedProperty::try_from_str to FFI

Spawned off of https://github.com/unicode-org/icu4x/issues/6049.

We have [`NamedEnumeratedProperty::try_from_str()`](https://unicode-org.github.io/icu4x/rustdoc/icu_properties/props/trait.NamedEnumeratedProperty.html#method.try_from_str) but this does not appear to be available on FFI.