Fix Paste without Formatting / Paste and Match Style producing uneditable text nodes.

[Killavus]

Is this adding or improving a feature or fixing a bug?

Fixing a bug.

What's the new behavior?

This fixes #3414. Basically right now Paste and Match Style type of pasting from Chrome is working properly - as well as mod+shift+v shortcut from other browsers.

How does this change work?

Since these types of pastes are not emitting beforeinput events, I handle them in paste event handler. After that it's just a matter of simply passing them to insertData of ReactEditor. I want to minimize the surface area of change, so this behavior is triggered only for pastes having exclusively text/plain ClipboardData in them.

Have you checked that...?

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)

Does this fix any issues or need any specific reviewers?

Fixes: #3414
Reviewers: @