fix: __INTLIFY_PROD_DEVTOOLS__ is not defined (#532)

closes #529

Author: kazupon

packages/core-base/src/index.ts

@@ -1,3 +1,5 @@
+import { getGlobalThis } from '@intlify/shared'
+
 export * from '@intlify/message-resolver'
 export * from '@intlify/runtime'
 export {
@@ -14,3 +16,9 @@ export { getWarnMessage, CoreWarnCodes } from './warnings'
 export { CoreError, CoreErrorCodes, createCoreError } from './errors'
 export * from './types'
 export * from './devtools'
+
+if (__ESM_BUNDLER__ && !__TEST__) {
+  if (typeof __FEATURE_PROD_INTLIFY_DEVTOOLS__ !== 'boolean') {
+    getGlobalThis().__INTLIFY_PROD_DEVTOOLS__ = false
+  }
+}