Make extension data JSON-serializable #2 - write JSON.
Make extension data JSON-serializable #2 - write JSON.

Switching ParserCache to JSON serialization requires
extensions to stop writing non-JSON-serializable objects
into ParserOutput::setExtensionData.

NOTE: This should be merged at least 1 train after the parent
change that introduces forward compatibility!

Bug: T266260
Change-Id: I9fc7f5554896d16751f05e1f9fcfdf6bd78365a3

wikimedia/mediawiki-extensions-Kartographer,wikimedia/mediawiki-extensions-Kartographer,wikimedia/mediawiki-extensions-Kartographer