Updated design of collapse button in widget extensions

What does this MR do and why?

Changes the designs of the collapse button inside of widget extensions.

Screenshots or screen recordings

How to set up and validate locally

• View any merge request widget to see an extension with test data

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.