Merge fallback locales in lizDict

[Gustry]

New PR like #5139 or #5131 adding new strings in lizDict are missing translations when using LWC in another language than English, until we do the update with Lizmap locales process.

I'm clearly not sure if it's the purpose in this file to add the fallback, or if it must be done elsewhere, upstream etc.

[laurentj]

LGTM. LocalesLoader is using low level api of JLocale, so, no, we cannot backport it in upstream.

Note that this patch cannot be backported to lizmap 3.8 as 3.8 does not use low level api of jLocale, but use its own parser that is not very reliable (and does not take advantage of cache used by jLocale)

[Gustry]

I'm not fully sure about the last talks we got in the chat about this PR.
Indeed, the best should be on "build" time, to add all missing strings in each languages, to English.
But then, it means the ZIP would fallback on English by default anyway, despite the setting in INI file. Or this PR should be done only if the fallback is different than en_US to avoid loading two files.

Side note, this dictionary file doesn't seem "too big", like 200 lines lizmap/modules/view/locales/en_US/dictionnary.UTF-8.properties.