More Like This Params Refactor [LUCENE-8326]

More Like This ca be refactored to improve the code readability, test coverage and maintenance.
Scope of this Jira issue is to start the More Like This refactor from the More Like This Params.
This Jira will not improve the current More Like This but just keep the same functionality with a refactored code.

Other Jira issues will follow improving the overall code readability, test coverage and maintenance.

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Migrated from [LUCENE-8326](https://issues.apache.org/jira/browse/LUCENE-8326) by Alessandro Benedetti (@alessandrobenedetti), updated May 17 2019
Attachments: [LUCENE-8326.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-8326/LUCENE-8326.patch) (versions: 4)
Linked issues:
- #8853
- [SOLR-12304](https://issues.apache.org/jira/browse/SOLR-12304)

Pull requests: https://github.com/apache/lucene-solr/pull/369

Start with the More Like This Params area and review the attached LUCENE-8326.patch to understand the intended refactor boundaries. Check linked issue #8853 and the referenced pull request before proceeding. Done means preserving current More Like This functionality while improving readability, maintenance, and test coverage.

Written by the indexing model from the issue text.