Note: the method is named getNewTermStoreWriterFactory(), and always returns a new instance (i.e. there’s no $this->termStoreWriterFactory), but I suspect the “new” in the name is meant as “new term store” (aka the “2019 term store”, or just “the term store” now that we got rid of the “old” one in Wikibase wb_terms leftovers 2020), not “always returns a new instance”, and so it should be okay to move it to the service container.

Can be done after T276430: Move WikibaseRepo StringNormalizer to service container.