Merge trivial JDWP agent changes from the loom repo to the jdk repo

In the loom repo there are a number of trivial changes to the JDWP agent that are not loom specific. Moving them to the jdk repo will make future merges simpler, along with making it easier to get a diff of the important differences between the loom and jdk repos, without the clutter of these trivial changes. The changes I'd like to merge are:

1. Very minor code refactoring.
2. Comment additions, fixes, and improvements.
3. Minor indentation and whitespace changes.
4. Added a trivial assert