Describe the bug

Markdown editor components whose field's have a pattern option will crash the UI when calling setInactiveStyle due to a call to this.props.onValidate within the this.validate function on the Widget component.
https://github.com/netlify/netlify-cms/blob/30c11954d586c43a00c8c61fa467873bfe1ed1fc/packages/netlify-cms-core/src/components/Editor/EditorControlPane/Widget.js#L129

The error that occurs is this.props.onValidate is not a function

The prop onValidate is not a required prop. It should either have a default value or be wrapped in an if statement:

if (this.props.onValidate) {
  this.props.onValidate(errors);
}

The issue occurs because the markdown editor component's component (Shortcode) does not pass an onValidate function to the EditorControl.
https://github.com/netlify/netlify-cms/blob/89848e034451baed52fb8911d3778a2f469462f8/packages/netlify-cms-widget-markdown/src/MarkdownControl/components/Shortcode.js#L37

To Reproduce

1. Add a custom editor component with a field that has a pattern.
2. Add the custom editor component to the editor component list of a markdown field.
3. From the editor component dropdown, select your custom editor component
4. Insert some data into the field with the pattern
5. De-focus the input
6. Should crash (for some reason this takes a second or 2)

Expected behavior

Using a custom editor component with a pattern option on a field should not crash the UI. Ideally, the onValidate function should not be called if it doesn't exist.

Applicable Versions:

• Netlify CMS version: 2.14.3 (netlify-cms-app)
• Git provider: Gitlab
• OS: Linux Debian 10
• Browser version: Chrome 87
• Node.JS version: 10

CMS configuration

The full config.yml is too large to efficiently show/link to. Ive included a custom editor component that is causing errors
https://gist.github.com/Pearce-Ropion/6d806e98c30206639e43e7ceb7a28e05

Additional context

My guess is this error is caused by other dynamic widgets too. But I only followed the code for editor components.