fix[react-devtools-standalone]: define missing globals (facebook#32327)

Same as what we did for `react-devtools-fusebox` in
facebook#32297.

Author: hoxyq

packages/react-devtools-core/webpack.standalone.js

@@ -88,6 +88,9 @@ module.exports = {
       __PROFILE__: false,
       __TEST__: NODE_ENV === 'test',
       __IS_NATIVE__: true,
+      __IS_FIREFOX__: false,
+      __IS_CHROME__: false,
+      __IS_EDGE__: false,
       'process.env.DEVTOOLS_PACKAGE': `"react-devtools-core"`,
       'process.env.DEVTOOLS_VERSION': `"${DEVTOOLS_VERSION}"`,
       'process.env.EDITOR_URL': EDITOR_URL != null ? `"${EDITOR_URL}"` : null,