Support GitLab's extended syntax

[jasonsperske]

I've been working on an update to https://marketplace.visualstudio.com/items?itemName=jasonnutter.vscode-codeowners to work better with the GitLab instance I use at work, and since the logic for that extensions is mostly in this library, I started here. This PR makes the following changes based on the rules outlined in https://docs.gitlab.com/ee/user/project/codeowners/reference.html

• Supports [Sections] with default owners (adds tests for this)
• Supports paths with escaped spaces
• Supports inline comments
• Adds a bunch of tests
• Updates to use mjs imports as opposed to commonjs requires (this one was mostly to keep the code in line with the rest of my job's coding style, but if it's not what you want, I can roll it back)

The updated extension I've built with these changes can be found at https://github.com/jasonsperske/vscode-codeowners but if you accept these changes, then I can just depricate my extension because all of these changes work seamlessly inside of the current CODEOWNERS extension by @jasonnutter.

Let me know if you want me to refactor anything.