Merge pull request #2091 in HDFFV/hdf5 from ~NFORTNE2/hdf5_naf:hdf5_1_12 to hdf5_1_12
* commit '1b45a5c09f7f31dfc6920c3fe503b8e043e327a2':
Add RELEASE.txt note for HVLget_file_type()
Implement H5VLget_file_type() to return a copy of a datatype with the location set to be in a file. Only meant to be used by VOL connectors. Implement H5VLpeek_connector_id() to support connectors querying their own IDs. Fix app_ref with connector IDs in a couple places (external VOLs registered as default through ENV should be visible to the application). Modify vlen and reference interfaces to work with arbitrary VOL connectors. Implement file "post open" specific callback, to enable connectors to update their file structs after a wrap context has been set.
