scratch-gui bundled react and react-dom in its production build

[xuanduc987]

Expected Behavior

scratch-gui should not bundled react and react-dom package, so that the application ussing scratch-gui could provide its own version of react

Actual Behavior

From #9536, the externals of webpack config had been removed. If this was unintentional changed, I believe it should be added back (the rationale for this would be the same as the one in this PR #6754)