Avoid storing ignored source for multi-fields

[kkrik-es]

in case of multi-fields, the "parent" field is responsible for tracking the source. Other fields should not track source, e.g. in case of a keyword exceeding the ignore_above limit.

This was partially addressed in #129126 but needs to be generalized.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)