Add U_ error constants to intl constant list

[haszi]

Add missing U_ error constants to intl constant list. All of these are listed on the missing constant list (#2747).

Edit: I used the following script which can also be used to update all translations: https://gist.github.com/haszi/66f36bc412323e0365b8614aeabaa816 Please note that the scripts unconditionally adds the constants to the constants page, ie. without checking whether these are already present so running it more than once is not advised.