The file-per-definition style should name files using similar conventions as IGP

From Saul Kravitz:

> It would be very helpful if the names of the files in input/fsh/instances were similar to the JSON files output by the IGP, and included the FHIR resource type. For example: `Observation-CauseOfDeathPart1-Example1.fsh` instead of the current `CauseOfDeathPart1-Example1.fsh`. There is no easy way to map backwards to make that association from the generated FSH output.

I think we should consider doing this for all resource in the file-per-definition style (not just instances).