Update JSX button code to use new syntax

• Type: Bug
• Status: KM Review In Progress
• Priority: Minor
• Resolution: Unresolved
• Fix Version/s: 7.0.x
• Component/s: Product Team Frontend Infrastructure
• Labels: None
• Type of Documentation: Developer
• Git Pull Request: https://github.com/sez11a/liferay-docs/pull/4808

Following this page tutorial for creating a new button for 7.0 fix pack 89 didn't work.
after initial investigation we realize that indeed mixins are not available starting with alloyeditor version 2
 
If the user wants to use mixins he needs to upgrade to at least alloyeditor version 2.11.0,
which is included started with fix pack 90, see https://issues.liferay.com/browse/LPS-102881 related to this update
 
the error user was facing is related to the part of creating the button https://help.liferay.com/hc/en-us/articles/360017882692-Creating-and-Contributing-new-Buttons-to-AlloyEditor#creating-the-button