Add support for the Modi script

Add support for the Modi script

* lisp/language/indian.el ("Modi"): New language environment.
Add composition rules for Modi.  Add sample text and input
method.
Add sample text to various scripts.
Rename Punjabi to Gurmukhi.
* lisp/international/fontset.el (script-representative-chars)
(setup-default-fontset): Support Modi.
* lisp/leim/quail/indian.el ("modi"): New input method.
(Bug#55439)

* etc/HELLO: Add a Modi greeting.
Rename Hindi to Devanagari.
Add a Gurmukhi greeting.
Replace Odia greeting.
* etc/NEWS: Announce the new language environment and its
input method.