Add input methods for Urdu, Pashto and Sindhi (bug#66470)

Add input methods for Urdu, Pashto and Sindhi (bug#66470)

* lisp/leim/quail/pakistan.el ("urdu-keyboard")
("urdu-phonetic-keyboard", "urdu-custom", "sindhi-keyboard")
("pashto-keyboard"): New input methods.
(pakistan--define-quail-rules, pakistan--make-setter)
(pakistan--regenerate-translations, pakistan--set-prefixes)
(pakistan--define-numeral-translations)
(pakistan--set-numeral-translations):
Internal helper functions.
(pakistan-urdu-input): New customization group.
(pakistan-urdu-prefixes, pakistan-urdu-translations)
(pakistan-urdu-diacritics-and-other-symbols)
(pakistan-urdu-poetic-symbols, pakistan-urdu-religious-symbols)
(pakistan-extra-balochi-brahui-translations)
(pakistan-extra-pashto-translations)
(pakistan-extra-sindhi-translations)
(pakistan-extra-saraiki-hindko-translations)
(pakistan-urdu-use-roman-digits): New custom variables.
(pakistan): New package.