fix: [#483] Add optional JSDOM dependency for Node

[jfelsinger]

closes #483

This PR adds jsdom as an optional dependency that can be detected and used in environments that don't have support for the browser-internal DOMParser.

Caveats: This also fixes the graphics component breaks I was running into when trying to run headless to actually test this. I can move that out into a separate Issue & PR if that makes sense to do. Essentially, I removed the loading of the actual image/sprite/animations when headless since it was breaking in Node when a browser graphic context wasn't there, even though headless would imply that not being necessary.

Usage

When planning to use excalibur-tiled in Node.js or another non-browser environment, include jsdom when installing excalibur-tiled...

npm i --save @excaliburjs/plugin-tiled@next jsdom

or any time after if it's needed.

npm i --save jsdom

[eonarheim]

@jfelsinger Looks like CI wants the package-lock.json

[jfelsinger]

Very weird, I thought I included that in the initial commit. Lock file updated & pushed.

[eonarheim]

@jfelsinger Pushed a commit to tweak the CI webpack config quick, all the tests passed locally so I expect to merge this momentarily!

[eonarheim]

@jfelsinger Many thanks for digging into this! Much appreciated! ⚔️