Implement file name handler for `file-name-case-insensitive-p'

Implement file name handler for `file-name-case-insensitive-p'

* doc/lispref/files.texi (Truenames): `file-name-case-insensitive-p'
is also applicable for remote hosts.

* lisp/net/tramp.el (tramp-methods): Improve docstring.
(tramp-file-name-for-operation): Add `file-name-case-insensitive-p'.
(tramp-handle-file-name-case-insensitive-p): New defun.

* lisp/net/tramp-smb.el (tramp-methods) <smb>:
Add `tramp-case-insensitive' entry.

* lisp/net/tramp-adb.el (tramp-adb-file-name-handler-alist)
* lisp/net/tramp-gvfs.el (tramp-gvfs-file-name-handler-alist)
* lisp/net/tramp-sh.el (tramp-sh-file-name-handler-alist)
* lisp/net/tramp-smb.el (tramp-smb-file-name-handler-alist)
<file-name-case-insensitive-p>: Add handler.  (Bug#22300, Bug#24441)