symbols/us: add remaining vowels with diaeresis to us-intl

Many "modern" international variants such as altgr-intl, altgr-weur, eurkey, carpalx-intl, etc. use their available real estate to finish binding the basic vowels with diaeresis that correspond to nearby vowels with acute on the layout.
This patch adds idiaeresis to the altgr levels of J and ediaeresis to the altgr levels of F which are the nearest unbound keys to I and E on a QWERTY layout.

For altgr-intl in particular, altgr+J is already accounted for, but ediaeresis has already been mapped to altgr+R instead, so rather than binding the same thing to J twice, it now masks the parent layout's binding for altgr+F so that the end layout remains unchanged.

carpalx-intl does not need any modification as it already has every keysym accounted for