types: mark options param of ImageryLayer.fromProviderAsync as optional

[NickCrews]

As the examples show, it is perfectly fine to not pass in the options object. However, in my typescript project, if I don't pass in the options, I get a type error. This is intended to fix that error.

This was brought up in https://community.cesium.com/t/error-when-initialize-imagerylayer-fromproviderasync-without-options/31665

I'm not used to typescript/jsdoc at all, so this might not actually be the right way to do this. If you tell me how to do this,
let me know and I can update it.

[github-actions]

Thank you for the pull request, @NickCrews! Welcome to the Cesium community!

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[NickCrews]

I just signed the CLA. I don't personally need myself in the contributors file. If YOU require me in there, I can add myself.

[jjspace]

Thanks for the PR! Just had one small comment.

If YOU require me in there, I can add myself.

Yes, if you could please add yourself that would be great 🙏

[NickCrews]

I added myself to contributors and adjusted the docstring. Thank you! @jjspace

[ggetz]

Thanks @NickCrews! Since this affects the TypeScript definitions, could you please add an item in CHANGES.md under "Fixes" with a short summary of the error that was fixed?

[NickCrews]

@ggetz done, thank you!

[ggetz]

Perfect, thanks @NickCrews!

Confirmed request changes were made.