getFlashMessages selector causes re-renders

[chawes13]

When using the useSelector hook, a console warning is shown instructing the user to memoize the result.

Since getFlashMessages returns new array, it will always trigger a re-render of its component (the default comparator is shallow equals, i.e., ===).

This is especially worrisome because it's usually included in the top Layout component within our client repos and will trigger a re-render after every action is handled and updates state somewhere in the tree, which could have a cascading effect on triggering child re-renders throughout the app.

Potential solutions:

• Don't export selectors
• Use createSelector from reselect to memoize the selectors