Add New String Interleave Class and Tests

[pdsla112]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

References

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Java files are placed inside an existing directory.
• All filenames are in all uppercase characters with no spaces or dashes.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[ayaankhan98]

Thanks for your contribution @pdsla112.
LGTM!

[pdsla112]

Wow! Thank you so much! Can I ask, when I check the master branch it doesn't show my Interleave class, but it shows in the Development branch. Is this how it's supposed to be for new contributions? I just followed the instructions for new contirbutions.