Fixes Color.fromCssColorString when color string contains spaces

[sambakk]

Fixes #9015

[cesium-concierge]

Thanks for the pull request @sambakk!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[hpinkos]

Thanks for the PR @sambakk! That was my only comment

[hpinkos]

Oh, also please add a comment about this to CHANGES.md under the Fixes section

[sambakk]

Thanks for the PR @sambakk! That was my only comment

You're welcome @hpinkos, I updated the PR as requested.

[hpinkos]

Thanks for the contribution @sambakk!