split the `import` method from `NoteCreateService` into its own file, and reduce code duplication between create/edit/import

git merge gets pretty confused by NoteCreateService because create and import are nearly identical, so often upstream changes get applied to import instead of create

We can split import into its own NoteImportService.

Then, to avoid having to copy all the smaller helper functions, we can have both NoteEditService and NoteImportService get an instance of NoteCreateService and call the helpers on that.

We can't do much to avoid copying the main body of the create method into import and edit, but we could factor out as much as we can between those two, since we control them. OTOH, having the three methods look very similar may help make sure we apply all upstream changes to all three…

added enhancement feedback wanted labels

mentioned in merge request !502 (closed)

removed feedback wanted label

added in progress label

import is essentially gone in 2024.8 (it just calls create with silent=true).

Sharing more code between NodeCreateService and NoteEditService would still be nice, though.