JSON materialization code should be resilient to incorrect JSON documents

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This JSON materialization code needs to be made resilient to malformed JSON content. In general, when reading JSON tokens, we should be defensive and immediately throw for any unexpected token. We should also do a pass over other JSON processing code (especially anything with flow control/loops) and ensure that it's resilient.

Note: this was discovered while porting JSON owned entity support to PostgreSQL (test JsonQueryAdHocTestBase.Junk_in_json_basic_no_tracking). At this point I'm still investigating what caused the incorrect JSON document, but we should be resilient to this in any case.

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Note: the Junk_in_json_basic_no_tracking failure on PG happened because of #32235, i.e. without having actual malformed JSON data in the database.