Mount EditorComponent as soon as ReactEditorView is constructed

...instead of waiting for it to be attached. This makes it simpler to
get shim references when using ReactEditorView for mini editors.
Use ReactEditorView in SelectListView when flag is enabled
Don't apply special styles React mini editors
Merge pull request #3071 from atom/ns-react-select-list-editor

Use React for select list mini editors when config option is toggled