Add iOS import functionality

[thomcc]

Fixes #1017

I've tested this locally on my bookmarks, and it works, but it needs real tests. It's also hard to test, since it's basically a big ol' mountain of SQL.

I also need to expose it over the FFI to iOS. Done.

Pull Request checklist

• Quality: This PR builds and tests run cleanly
  • cargo test --all produces no test failures
  • cargo clippy --all --all-targets --all-features runs without emitting any warnings
  • cargo fmt does not produce any changes to the code
  • ./gradlew ktlint detekt runs without emitting any warnings
  • Note: For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due dilligence applied in selecting them.

[bug-mirror]

cc @linacambridge

[linacambridge]

Great! Thanks for taking this, @thomcc! 💯