Added Roman to Integer

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
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https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/RomanToInteger.java It is already available. You could add some more test for this. There are only two.

Hi @debasishbsws, thank you for your comment. I have added few extra test cases for RomanToInteger.java code

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