Improve usability and documentation of Iroquoian input methods

Improve usability and documentation of Iroquoian input methods

* lisp/leim/quail/iroquoian.el: Add variants for Mohawk and Oneida
endonyms in comments and docstrings.  Update the 'oneida-postfix' input
method to make the most commonly used glottal stop character easiest to
input.  Update the 'onondaga-postfix' input method with mnemonic keys
for nasals in the Onondaga Nation, New York orthography.  (Bug#75448)

* etc/NEWS: Add variants for Mohawk and Oneida endonyms to NEWS entry.

(cherry picked from commit edec6e2264ec4269d3bcdc5fadc22c793f5af7c2)