Issues with RecurMergeSort

[phrdang]

Where it's located

• Chapter: 13
• Section: 13.6
• Problem Title: Merge Sort

Describe the issue

• RecurMergeSort.java practice and solution files are not named MergeSort.java to match the problem name (doesn't follow practice problem guidelines)
• The files also do not contain the instructions of the problem
• The instructions of the problem are extremely sparse and require students to figure out both the Merge Sort algorithm, the Comparable class, and generics on their own
• The files raise the following warnings on VSCode that should be fixed:

Notes

Make sure to fix not just the code in the repo but also the problem statement and links on Notion.
Also see #15 for the original PR