[RFR] Add auth hooks

[fzaninotto]

• [BC Break] Store authProvider in modern React context instead of legacy context
• Add useAuth() hook (replacement for <Authenticated>)
• Add usePermissions() hook (replacement for <WithPermissions>)
• use usePermissions instead of WithPermissions in <Resource> (we need an intermediate component because hooks can't execute inside a render function)
• Use the new hooks in examples
• Update documentation
• Update upgrade guide

import { useAuth } from 'react-admin';

const CustomRoutes = [
    <Route path="/foo" render={() => {
        useAuth();
        return <Foo />;
    }} />,
    <Route path="/bar" render={() => {
        const { authenticated } = useAuth(
            { myContext: 'foobar' }, 
            { logoutOnFailure: false }
        );
        return authenticated ? <Bar /> : <BarNotAuthenticated />;
    }} />,
];
const App = () => (
    <Admin customRoutes={customRoutes}>
        ...
    </Admin>
);

import { usePermissions } from 'react-admin';

const PostDetail = props => {
    const { loaded, permissions } = usePermissions();
    if (loaded && permissions == 'editor') {
        return <PostEdit {...props} />
    } else {
        return <PostShow {...props} />
    }
};

[fzaninotto]

Switching to RFR

[djhi]

🔥