build: export runtime-only build for bundlers by default in main vue package

packages/vue/src/devCheck.ts

@@ -0,0 +1,6 @@
+if (__BROWSER__ && __DEV__) {
+  console[console.info ? 'info' : 'log'](
+    `You are running a development build of Vue.\n` +
+      `Make sure to use the production build (*.prod.js) when deploying for production.`
+  )
+}

packages/vue/src/index.ts

@@ -1,4 +1,4 @@
-// This package is the "full-build" that includes both the runtime
+// This entry is the "full-build" that includes both the runtime
 // and the compiler, and supports on-the-fly compilation of the template option.
 import { compile, CompilerOptions, CompilerError } from '@vue/compiler-dom'
 import { registerRuntimeCompiler, RenderFunction, warn } from '@vue/runtime-dom'
@@ -61,9 +61,4 @@ registerRuntimeCompiler(compileToFunction)
 export { compileToFunction as compile }
 export * from '@vue/runtime-dom'
 
-if (__BROWSER__ && __DEV__) {
-  console[console.info ? 'info' : 'log'](
-    `You are running a development build of Vue.\n` +
-      `Make sure to use the production build (*.prod.js) when deploying for production.`
-  )
-}
+import './devCheck'

packages/vue/src/runtime.ts

@@ -0,0 +1,6 @@
+// This entry exports the runtime only, and is built as
+// `dist/vue.esm-bundler.js` which is used by default for bundlers.
+
+export * from '@vue/runtime-dom'
+
+import './devCheck'