Synthetic source: avoid storing copy_to text or match_only_text target field by default

[martijnvg]

If a copy field target field is of type of either text or match_only_text, then don't default store mapping attribute to true when source mode is synthetic.

Originated from #129126

[elasticsearchmachine]

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

[Kubik42]

This is no longer necessary as it has been indirectly addressed by #132962. The default store value for text fields and match only text fields is now always false for new indices.