Merge styles with Choice custom styles

[ahnucl]

Allow selected and highlighted styles to work with Choice custom styles.

What is the problem that this PR addresses? I needed the hightlighting functionality with custom styles no my Choices.

https://github.com/tmbo/questionary/issues/151 ...

How did you solve it? I found that when the title param on Choice is a list it just extend the styles not checking if selected or hightlighted exists

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Checklist

• [ ] I have read the Contributor's Guide.
• [ ] I will check that all automated PR checks pass before the PR gets reviewed.

[kiancross]

@ahnucl Please can you update this branch with latest changes from master and then I will review.