Display Page Templates do not consider mapping type when discarding draft

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: Master
• Fix Version/s: Master
• Component/s: WCM
• Labels: None
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/71961

Description
Normally discard draft expects the page to revert to the exact state it was when you last published it. However what happens in the case that the user did not set the mapping type, but you set it after? It becomes impossible to truly revert back since you cannot revert the mapping type currently in display page templates. This can be very problematic if you accidently choose the wrong mapping type.

Steps to Reproduce

1. Create a Display page templates with some fragments
2. Publish
3. Change mapping type
4. Discard Draft

Expected Result
Mapping type returned to normal

Actual Result
Nothing happens

Tested on Tomcat 9.0.17 + MySQL 5.7
Portal master GIT ID: cd778159969289540f3e8a2793c83b2824f00ef2