SOLR-16427: Enable error-prone PatternMatchingInstanceof rule

[malliaridis]

https://issues.apache.org/jira/browse/SOLR-16427

Description

With the new errorprone rules and starting from 16+ we can use pattern-matching for instanceof.

Solution

This PR enables PatternMatchingInstanceof and applies auto-refactoring from IntelliJ for pattern-matching cases.

Note that these changes are not backwards compatible (branch_9x) as the refactored code makes use of a JDK 16 feature.

Tests

No tests were added or removed. Tests with pattern-matching improvements were refactored accordingly.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended, not available for branches on forks living under an organisation)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[malliaridis]

Waiting for #2877 to rerun the checks and merge afterwards.