feat(core): add genesis API (#14223)

Co-authored-by: Amaury <1293565+amaurym@users.noreply.github.com>

core/appmodule/genesis.go

@@ -0,0 +1,41 @@
+package appmodule
+
+import (
+	"context"
+	"io"
+)
+
+// HasGenesis is the extension interface that modules should implement to handle
+// genesis data and state initialization.
+type HasGenesis interface {
+	AppModule
+
+	// DefaultGenesis writes the default genesis for this module to the target.
+	DefaultGenesis(GenesisTarget) error
+
+	// ValidateGenesis validates the genesis data read from the source.
+	ValidateGenesis(GenesisSource) error
+
+	// InitGenesis initializes module state from the genesis source.
+	InitGenesis(context.Context, GenesisSource) error
+
+	// ExportGenesis exports module state to the genesis target.
+	ExportGenesis(context.Context, GenesisTarget) error
+}
+
+// GenesisSource is a source for genesis data in JSON format. It may abstract over a
+// single JSON object or separate files for each field in a JSON object that can
+// be streamed over. Modules should open a separate io.ReadCloser for each field that
+// is required. When fields represent arrays they can efficiently be streamed
+// over. If there is no data for a field, this function should return nil, nil. It is
+// important that the caller closes the reader when done with it.
+type GenesisSource = func(field string) (io.ReadCloser, error)
+
+// GenesisTarget is a target for writing genesis data in JSON format. It may
+// abstract over a single JSON object or JSON in separate files that can be
+// streamed over. Modules should open a separate io.WriteCloser for each field
+// and should prefer writing fields as arrays when possible to support efficient
+// iteration. It is important the caller closers the writer AND checks the error
+// when done with it. It is expected that a stream of JSON data is written
+// to the writer.
+type GenesisTarget = func(field string) (io.WriteCloser, error)