refactor: renamed package geocoding_ios to geocoding_darwin

[OutdatedGuy]

Renames geocoding_ios to geocoding_darwin to later add macOS support. Will follow up with macOS support PR after this is merged.

resolves #244

Pre-launch Checklist

• I made sure the project builds.
• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is does not need version changes.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I rebased onto main.
• I added new tests to check the change I am making, or this PR does not need tests.
• I made sure all existing and new tests are passing.
• I ran dart format . and committed any changes.
• I ran flutter analyze and fixed any errors.

[mvanbeusekom]

Hi @OutdatedGuy,

Recently we have started refactoring the platform interface package and I have a PR open (see #278).

As part of this I have also already created a Darwin implementation based on the new interface (PR will be published soon).

I expect to land these PRs soon as they offer more finegrained control and resolve several other issues reported and supports the new MapKit SDK which will replace the by Apple deprecated CLGeocoder SDK.

Unfortunately this means this PR becomes obsolete, which pains me to say as you've put a considerable amount of time into it.

[OutdatedGuy]

No worries as long as the plugin is maintained and gets macOS support. Thanks for the update @mvanbeusekom