Add the compliant "Direct" doc-value format [LUCENE-10251]

In an effort to keep the "Direct" doc-value format in future release, we moved them to doc-value iterators. Any review would be appreciated.

Main changes include:
- Use DocValuesIterator instead of LegacyDocValues.java in DirectDocValuesProducer;
- Embed iterator implementation inside DirectDocValuesConsumer for code reuse;
- All test cases have been run successfully and included in [pull request](https://github.com/apache/lucene/pull/464/files);

P.S. Our business scenario:
- Save the inventory in Direct doc-value format;
- Update them in memory with high-frequency without persistence;
- Load inventory from data storage during app ignite;

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Migrated from [LUCENE-10251](https://issues.apache.org/jira/browse/LUCENE-10251) by spike liu, updated Jan 18 2022
Attachments: [compliant_direct_doc-value_format.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-10251/compliant_direct_doc-value_format.patch), [LUCENE-10251-20211222.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-10251/LUCENE-10251-20211222.patch), [LUCENE-10251-20211231.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-10251/LUCENE-10251-20211231.patch)
Linked issues:
- #9960
- #11372

Pull requests: https://github.com/apache/lucene/pull/464, https://github.com/apache/lucene/pull/464

Start by reviewing DirectDocValuesProducer, LegacyDocValues.java, and the iterator implementation in DirectDocValuesConsumer, then compare the attached patches and pull request 464. Done means the Direct doc-value format uses DocValuesIterator as described and the existing test suite passes.

Written by the indexing model from the issue text.