Patch for making some variable names more consistent with the other parts of the code. [LUCENE-9019]

Hello, we're developing an automated system that detects inconsistent variable names in a large software project. Our system checks if each variable name is consistent with other variables in the project in its usage pattern, and proposes correct candidates if inconsistency is detected. This is a part of academic research that we hope to publish soon, but as a part of the evaluation, we applied our systems to your projects and got a few interesting results. We carefully reviewed our system output and manually created a patch to correct a few variable
names. We would be delighted if this patch is found to be useful. If you have a question or suggestion regarding this patch, we'd happily answer. Thank you.

P.S. our patch is purely for readability purposes and does not change any functionality. A couple of issues that we've noticed were left untouched. For example, mixed use of variable names "len" and "length" were fairly widespread, but we have only corrected a few notable
instances to minimize our impact.

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Migrated from [LUCENE-9019](https://issues.apache.org/jira/browse/LUCENE-9019) by Yusuke Shinyama (@euske)

The issue describes a readability-only variable-name patch but names no files, classes, tests, or concrete identifiers to change. First locate the original LUCENE-9019 patch or its referenced changes, then inspect the affected Java code and run the relevant existing tests; done means the specified names are consistent without changing behavior.

Written by the indexing model from the issue text.