Update nest host determination in line with latest proposed JVMS changes for JEP-371

Attached Draft-JVMS-JEP-371.pdf shows the latest JVMS proposal.

Key changes: access checks will no longer throw LinkageErrors or other errors related to nest host resolution and validation. If such an error occurs the result is that the class becomes its own nest host and the access check will fail with IllegalAccessError.

Existing tests will need updating to not expect exceptions, but instead check logging output.

Will also investigate if it is feasible to report any underlying error as a "cause" of the IllegalAccessError.