Term vectors options should not be configurable per-doc [LUCENE-9078]

Make term vectors constant across the index. Remove the user ability to modify the term vector options per doc, IndexWriter allows this.

Once done, consider removing Fields, as the list of fields could be obtained from FieldInfos. See the discussion in #9089.

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Migrated from [LUCENE-9078](https://issues.apache.org/jira/browse/LUCENE-9078) by Bruno Roustant (@bruno-roustant), 2 votes, updated Mar 15 2021
Linked issues:
- #10374
- #9089

Start by reading how IndexWriter currently permits per-document term vector options, then review the discussion in #9089 and the linked issue #10374. Done means term vector options are constant across the index and users can no longer modify them per document; consider the separately mentioned removal of Fields only after that scope is understood.

Written by the indexing model from the issue text.