FI-2354: bump core validator library to 6.2.8

[dehall]

Summary

This PR bumps the internal hl7 validator library version to the latest - 6.2.8. The main driver for this is US Core 7 support.

There were a few minor changes needed:

• A couple classes moved around so references were updated: VersionUtil and FhirPathEngine
• BaseValidator constructor now requires that the "context" passed in not be null, so I passed in the context from a ValidatorEngine instance we already had. The BaseValidator is not actually used anywhere, it's just necessary to have an instance to get access to the ValidationControl internal class, so there should be no impact to this.
• FilesystemPackageCacheManager now uses a Builder instead of public constructors. The boolean parameter before was for "userMode" which determined the cache directory used : https://github.com/hapifhir/org.hl7.fhir.core/blob/6.0.21/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/npm/FilesystemPackageCacheManager.java#L123
  Now the default is to use the user directory https://github.com/hapifhir/org.hl7.fhir.core/blob/6.2.8/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/npm/FilesystemPackageCacheManager.java#L122

Testing Guidance

The US Core 7 package can be downloaded from https://build.fhir.org/ig/HL7/US-Core/downloads.html
Place this in the ./igs folder and start the server, validate some resources, confirm it all works

[Jammjammjamm]

Unfortunately, this update causes validation errors in g10. It seems fine in US Core, so this is a new error when not using a terminology server. Looks like we'll have to add another filter in the g10 tests.