Fix contains method to use .contains for DOMTokenList

[Dakkers]

What does this PR do?

Fixes a bug I ran into. I had custom style tags, whose value and tag were "div". When I selected some text and changed the style tag to be one of these "div" styles, and then hit "Enter" a couple of times, I got .indexOf is not a function.

Where should the reviewer start?

There's only 1 file.

How should this be manually tested?

1. use a custom style tag that doesn't map to a header tag (I used a div)
2. highlight some text
3. use the custom style tag
4. de-select
5. hit Enter a couple of times
6. error shows in console

example custom style tags:

styleTags: [
  { title: 'BV Title 1', tag: 'h1', className: 'bv-title-1', value: 'h1' },
  { title: 'BV Title 2', tag: 'div', className: 'bv-title-2', value: 'div' },
  { title: 'BV Title 3', tag: 'div', className: 'bv-title-3', value: 'div' },
  { title: 'BV Title 4', tag: 'div', className: 'bv-title-4', value: 'div' },
  { title: 'BV Title 5', tag: 'div', className: 'bv-title-5', value: 'div' }
]

in this case, the "BV Title 1" works just fine. "BV Title 2" and others do not.

Any background context you want to provide?

N/A

What are the relevant tickets?

Not sure.

Screenshot (if for frontend)

Checklist

• added relevant tests
• didn't break anything
• ...

[hackerwins]

@Dakkers Thanks for the contribution.