fusefs: implement VOP_ACCESS

fusefs: implement VOP_ACCESS

VOP_ACCESS was never fully implemented in fusefs.  This change:
* Removes the FACCESS_DO_ACCESS flag, which pretty much disabled the whole
  vop.
* Removes a quixotic special case for VEXEC on regular files.  I don't know
  why that was in there.
* Removes another confusing special case for VADMIN.
* Removes the FACCESS_NOCHECKSPY flag.  It seemed to be a performance
  optimization, but I'm unconvinced that it was a net positive.
* Updates test cases.

This change does NOT implement -o default_permissions.  That will be handled
separately.

PR:		236291
Sponsored by:	The FreeBSD Foundation