[IR] Generate proguard rule files

[ZacSweers]

Unclear how this could work, if at all

[ZacSweers]

Worst case we could implement that in AnalysisHandlerExtension, but then it's sort of two plugins in one. Maybe it's opt-in at that point

[ZacSweers]

I think AnalysisHandlerExtension is the way to go for now.

Requires

• Gradle plugin to manage/handle setting up generated resources and wiring them appropriately for projects (see prior art in KSP)
• Extension that handles incrementalism and finds all JsonClass-annotated classes. Skip checks other than checking generateAdapter and generator properties.
• Extension needs to support sealed and regular. Functionally the same.