Rename LatestVersionMergePolicy for a more intuitive name compatibility with the factory

[rahulgoswami]

Description

The factory name is LatestVersionMergePolicyFactory, whereas the policy is named LatestVersionFilterMergePolicy. Also the name indicating it’s a FilterMergePolicy is really an implementation detail we can do away with.

Solution

Rename LatestVersionFilterMergePolicy to LatestVersionMergePolicy.

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
• I have added a changelog entry for my change

[rahulgoswami]

@dsmiley @gerlowskija Mind taking a look please? Thanks.

[rahulgoswami]

fwiw this merge policy is currently merged but unreleased across branch_9x, branch_10x and branch_10_0, so should be a safe change.