Cleanup asdf.util

[braingram]

Description

This PR starts the cleanup of the asdf api starting with the asdf.util submodule. This PR includes the following deprecations:

• deprecate human_list (unused in downstream)
• deprecate resolve_name and minversion (these are out-dated copies from astropy.utils, the one use in the asdf pytest plugin was replaced, these methods are unused in downstream)
• deprecate iter_subclasses (unused in downstream, replaced with _iter_subclasses for internal uses)

The following were not listed in __all__ and are only used internally. Each was modified to be prefixed with an _ to make their private nature more explicit:

• BinaryStruct
• InheritDocstrings
• patched_urllib_parse

One addition was made to the public api:

• add get_file_type and FileType to __all__ (these are used by weldx and look generally useful for working with ASDF files as a way to check if a file is an ASDF file without some sort of try/except with asdf.open)

Once merged, tracking issues can be opened for the deprecations to plan for their removal in asdf 4.0.

Checklist:

• pre-commit checks ran successfully
• tests ran successfully
• for a public change, a changelog entry was added
• for a public change, documentation was updated
• for any new features, unit tests were added