[SDK-2106] Memoize auth methods

[adamjmcgrath]

(will base on master after #146 is merged)

Description

Memoizing the auth methods means that downstream components that use them in dependent keys of other hooks wont get unnecessary updates when auth state changes.

*Easier to review if you hide whitespace changes https://github.com/auth0/auth0-react/pull/150/files?w=1

References

Fixes #131

Testing

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[frederikprijck]

I love this, I added a comment but I don't think it is blocking.

[frederikprijck]

Even tho this is mostly just testing that we are using useCallback and that it is working as expected, I actually like this test.
Would it make sense to add a test for the other functions as well?

Could probably make it a single test:

[
  { name: 'getIdTokenClaims', cb: (provider) => provider.getIdTokenClaims },
  { name: 'loginWithRedirect', cb: (provider) => provider.loginWithRedirect },
].forEach(({name, cb}) => 
  it(`should memoize the ${name} method`, async () => {
    const wrapper = createWrapper();
    const { waitForNextUpdate, result, rerender } = renderHook(
      () => useContext(Auth0Context),
      { wrapper }
    );
    await waitForNextUpdate();
    const memoized = cb(result.current);
    rerender();
    expect(cb(result.current)).toBe(memoized);
  })
);

[adamjmcgrath]

Good idea - I'd do this but my IDE doesn't like dynamically creating tests - it doesn't let me run them from the gui. (I know that shouldn't stop me from doing it, but I really like running my tests like that 🤷)