Support abbreviating home directory of Tramp filenames

Support abbreviating home directory of Tramp filenames

* doc/lispref/files.texi (Magic File Names): Mention
'abbreviate-file-name' in the list of magic file name handlers.

* etc/NEWS: Announce the change.

* lisp/files.el (file-name-non-special):
* lisp/net/tramp.el (tramp-file-name-for-operation):
* lisp/net/tramp-sh.el (tramp-sh-file-name-handler-alist):
* lisp/net/tramp-smb.el (tramp-smb-file-name-handler-alist):
* lisp/net/tramp-sudoedit.el (tramp-sudoedit-file-name-handler-alist):
Add 'abbreviate-file-name'.

* lisp/files.el (directory-abbrev-make-regexp):
(directory-abbrev-apply): New functions.
(abbreviate-file-name): Check for file name handler.

* test/lisp/net/tramp-tests.el (tramp-test07-abbreviate-file-name):
New test.