Make application configurable in 'with-connection-local-variables'

Make application configurable in 'with-connection-local-variables'

* doc/lispref/variables.texi (Connection Local Variables):
Explain 'connection-local-default-application'.

* etc/NEWS: Mention 'connection-local-default-application'.

* lisp/files-x.el (connection-local-default-application): New variable.
(connection-local-criteria-for-default-directory): Use it.  (Bug#54405)

* test/lisp/files-x-tests.el
(files-x-test-with-connection-local-variables): Extend test.