feat(orm): ModuleDB JSON import/export/default/validate methods (#11101)

* feat(orm): ModuleDB JSON methods

* WIP

* WIP on JSON

* WIP

* WIP

* tests and docs

* revert

* tests and docs

* docs

* address review comments

orm/testing/ormtest/membackend.go

@@ -0,0 +1,18 @@
+// Package ormtest contains utilities for testing modules built with the ORM.
+package ormtest
+
+import (
+	"github.com/cosmos/cosmos-sdk/orm/internal/testkv"
+	"github.com/cosmos/cosmos-sdk/orm/model/ormtable"
+)
+
+// NewMemoryBackend returns a new ORM memory backend which can be used for
+// testing purposes independent of any storage layer.
+//
+// Example:
+//  backend := ormtest.NewMemoryBackend()
+//  ctx := ormtable.WrapContextDefault()
+//  ...
+func NewMemoryBackend() ormtable.Backend {
+	return testkv.NewSplitMemBackend()
+}