Local SPM development

[russhwolf]

Based on various conversations we've had in the community, it seems like there's a gap around local SPM development. KMMBridge was built for the use-case of publishing binary frameworks for remote SPM or Cocoapods consumption. The kotlin.cocoapods plugin helps with local Cocoapods development where the Pod builds Kotlin from source rather than consuming remotely. We have rudimentary support for doing local SPM development in KMMBridge, but it's not nearly as featureful as what's available from Kotlin for cocoapods. For example:

• It's possible to customize the podspec in the cocoapods plugin, but we don't have any Package.swift customization available currently
• The current local dev flow requires modifying the xcode project. It's easy to accidentally commit this change but it's almost always a bad idea
• The cocoapods plugin can pull in dependencies via cinterop, but there's nothing that does this for SPM right now.

We've done most of our development optimizing for the remote build use-case, targeting larger teams and projects. But there's clearly a need for a local SPM solution too. We want to do some thinking about this (though it's an open question whether it lives in KMMBridge or separate plugin). As we start to think about this, what are some other gaps that people would like to see filled?