features: Move migrations to their own source set.
features: Move codegen into src/codegen/java.
all: Convert .project/.classpath files to Gradle STS.
all: Gradle STS .settings files.
all: Other misc jdt settings changes.
starter: Fix migrations/codegen locations.
starter: Update gradle to build migrations separately.
features: Fix JoistCli/Registry dependency cycle.
all: Use build/eclipse for Eclipse class files.