chromium requires a custom format for hunspell dictionaries which
they provide as blobs in an upstream repository.
building from source (using convert_dict from the chromium monorepo
and applying it to already packaged dictionaries) would not yield
the same results (chromium packages adjustments to the dictionaries
themselves) and would increase the maintainance cost.
this patch adds a new hunspellDictsChromium attribute which includes
dictionaries from chromium.
