refactor test/inspector #13622

• Version: master
• Platform: all
• Subsystem: inspector

Especially now that it's not experimental, it seems that it would make sense to:

• move the tests in test/inspector into test/sequential and/or test/parallel as appropriate
• move the test/inspector/global-functions.js into test/fixtures
• move test/inspector-helper.js to test/common/inspector-helper.js

Basically, get rid of the inspector-specific directory.

Or is there real benefit to having it all in its own directory?

@nodejs/testing