[Side panel] update icon from X to chevron in expanded state (inline)

[kevinmweaver]

What package is this for?

• React

Describe the bug

In the inline variation of the side panel component, the button turns into an X when opened, it should remain a chevron.

Design guidance
https://pages.github.ibm.com/ai-applications/design/components/sidepanel/usage/#inline

To Reproduce

Steps to reproduce the behavior:
https://next.carbon-addons-iot-react.com/?path=/story/1-watson-iot-sidepanel--in-page-example