OPENNLP-1829: Transfer DirectoryModelFinder to OpenNLP core

[mawiesne]

Thank you for contributing to Apache OpenNLP.

In order to streamline the review of the contribution we ask you
to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

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Note:

Please ensure that once the PR is submitted, you check GitHub Actions for build issues and submit an update to your PR as soon as possible.

[rzo1]

@mawiesne "Error: Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:3.6.0:check (validate) on project opennlp-model-resolver: You have 4 Checkstyle violations. -> [Help 1]"