New macro connection-local-p

New macro connection-local-p

* doc/lispref/variables.texi (Applying Connection Local Variables):
Add macro 'connection-local-p'.

* etc/NEWS: Add macro `connection-local-p'.

* lisp/files-x.el (connection-local-p): New macro.
(connection-local-value): Add debug declaration.

* lisp/net/tramp-compat.el (tramp-compat-connection-local-p): New macro.

* lisp/net/tramp-crypt.el (tramp-crypt-cleanup-connection):
Bind `tramp-crypt-enabled'.

* test/lisp/files-x-tests.el (files-x-test-connection-local-value):
* test/lisp/net/tramp-tests.el (tramp-test18-file-attributes)
(tramp-test35-remote-path): Adapt tests.