Feat: use react component for dialogs instead of window alerts

[erezrokah]

Is your feature request related to a problem? Please describe.
There are several places in the code that use window.confirm/alert for dialogs (one example is when uploading an existing media file).

I think we should should consider switching to a friendlier UI (maybe we can use the existing redux-notifications package we're using for status messages).

Describe the solution you'd like
Use a react component for dialogs instead of window dialogs.

Describe alternatives you've considered
We can write our own modals but I'm guessing there should be a library for that.

Additional context
Related to this #2822

[Mack241]

There is an npm package called react-modal.

Alternative:
Using the Modal component API from Material-UI @erezrokah @erquhart

[erezrokah]

I think we'll be good with using an external package for this, as long as it's not deprecated/archived and gets security updates

[Mack241]

I have noticed that Editor, EditorToolbar and EditorInterface are class based components. Do you think changing it into functional components will be more efficient as we can use Hooks.
@erezrokah

[Mack241]

Or rather just EditorToolbar, since the Back-Arrow is present in this component.

[erezrokah]

Hi @Mack241, see my comment in #6137 (review) about using hooks in the CMS

[Mack241]

@erezrokah Got it!