SL-19078: add filename of emoji/shortcode XML files to ignore list so Viewer...

SL-19078: add filename of emoji/shortcode XML files to ignore list so Viewer checkouts don't appear to be polluted with files from 3p libs

.gitignore

@@ -56,6 +56,7 @@ indra/newview/teleport_history.txt
 indra/newview/typed_locations.txt
 indra/newview/vivox-runtime
 indra/newview/skins/default/html/common/equirectangular/js
+emoji_characters.xml
 indra/server-linux-*
 indra/temp
 indra/test/linden_file.dat