feat: provide ability to overwrite feature flags in esm-bundler builds

e.g. by replacing `__VUE_OPTIONS_API__` to `false` using webpack's
`DefinePlugin`, the final bundle will drop all code supporting the
options API.

This does not break existing usage, but requires the user to explicitly
configure the feature flags via bundlers to properly tree-shake the
disabled branches. As a result, users will see a console warning if
the flags have not been properly configured.

packages/vue/src/dev.ts

@@ -1,14 +1,14 @@
-import { version, setDevtoolsHook } from '@vue/runtime-dom'
+import { setDevtoolsHook } from '@vue/runtime-dom'
+import { getGlobalThis } from '@vue/shared'
 
 export function initDev() {
-  const target: any = __BROWSER__ ? window : global
+  const target = getGlobalThis()
 
-  target.__VUE__ = version
+  target.__VUE__ = true
   setDevtoolsHook(target.__VUE_DEVTOOLS_GLOBAL_HOOK__)
 
   if (__BROWSER__) {
-    // @ts-ignore `console.info` cannot be null error
-    console[console.info ? 'info' : 'log'](
+    console.info(
       `You are running a development build of Vue.\n` +
         `Make sure to use the production build (*.prod.js) when deploying for production.`
     )