fix: [#2622] Add multi engine support

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

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Closes #2622 Multi engine support is theoretically here!

There are some big changes here:

• TextureLoader is no longer a singleton, but an instance member on the ExcaliburGraphicsContextWebGL
• We defer loading textures into webgl until the first draw call, this is needed to in order to upload to the multiple contexts. This shouldn't cause too much of an issue since we only need to do this if the image ever changes.
• Additionally you must pass the gl context into the gl utility types

Needs a little more testing to make sure everything is still good. There is potentially some more refactoring opportunities as well to make this feel a little cleaner

Changes:

• Refactor TextureLoader to not be static
• Remove webgl adapter and pass gl context to gl helper types