Swaps epicsCoreJava pvAccess library for org.phoebus.core-pva

[jacomago]

Includes adding the tests:

• ChangedFieldsTest: Checks the metadata stored with the pv
• FlakyPVTest: Checks reconnects after connection drops
• GenericStructureTest: Checks the decoding and storage of a pvaStructure
• PauseResumeV4Test: Checks pausing and resuming a pv keeps it using the pvaccess protocol.
• PVAccessIntegrationTest: A basic integration test of using pvAccess to archive a pv
• PVAccessTypesTest: Test for each pvAccess type that it can be archived successfully.
• PVAFlakyIntegrationTest: Checks reconnects after connection drops
• PvaGetPVDataTest: Tests the retrieval api over pvAccess
• SamplePVATest: Basic unit tests of the pvaAccess library
• SampleV4PVAClientTest: Integration test of the pvAccess library
• GenericAnyStructureTest: Testing a generic structure with any values.
• FieldValuesCacheTest: Unit test for tracking meta data (other pvAccess fields) for pvAccess type.

Also reduces the default MIN_WRITE_PERIOD to speed up test running.

Adds support for more parts of pvAccess in the DBR_GENERIC_BYTES json formatter, including the Any type and the Union type.

Also adds support for tracking metafields the same way as channel access, by specifying fields in the policy.