Consider reexporting properties::props items in 2.0

[cmyr]

A quick note that while upgrading from 1.x to 2.x one change I had to address was that a lot of items that were previously available in the properties module (such as Script and BidiClass) are now in properties::props. Unless there's some compelling reason I'm missing, I think it makes sense to have these items available in the root properties module? It would make the upgrade experience cleaner for folks, and also provide a generally cleaner API.

[sffc]

This was discussed in #3573 and implemented in #5548

In general it makes the crate more organized for all property enums to be in a module together props, since icu_properties exports a bunch of other types for reading the properties. It is nice to see a list in one place.

CC @Manishearth @robertbastian Should we revisit this?

[Manishearth]

@cmyr The root of the module gets messy otherwise, we want it to have the main dataful types provided by the crate.