Changed type for some properties to Color from Property

[markchagers]

Fixes #9667. Some color properties of several Graphics classes (i.e. LabelGraphics.outlineColor) accept only a Cesium.Color, trying to set a ColorMaterialProperty has no effect at runtime. However the typescript definitions specify using a Property. This pull request attempts to address this by changing the type annotations for these properties. Going the other route: changing the implementation to work properly with a ColorMaterialProperty may be a better solution eventually, but is currently beyond my expertise.

[cesium-concierge]

Thank you so much for the pull request @markchagers! I noticed this is your first pull request and I wanted to say welcome to the Cesium community!

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[markchagers]

Please let me know if there is anything else that needs to be done before this PR can be evaluated. I have not changed or extended any tests because I'm not aware that any of these changes require it.

[srothst1]

@markchagers thank you for the pull request! We will look over this ASAP - I tagged a few other Cesium developers for a review.

Fixes #9667. This pull request stems from the following community forum thread.

@lilleyse
@ebogo1

[ebogo1]

Thanks @markchagers! This looks fine to me, just a couple nits in CHANGES.md.

@mramato Any objections to this change?

[mramato]

(i.e. LabelGraphics.outlineColor) accept only a Cesium.Color,

This is incorrect. These are Property instances, just not a MaterialProperty, i.e.

graphics.outlineColor = new ConstantProperty(Color.BLUE);
graphics.outlineColor = new SampledProperty(Color);

graphics.outlineColor = Color.BLUE; works but will result in graphics.outlineColor being a ConstantProperty (using implicit conversion borrowed from C#). Because of limitations in TypeScript, we can't tag properties as being multiple types. See this comment for some additional details: #8898 (comment)

If TypeScript has improved and we can better express implicity conversion, that would be awesome.

[markchagers]

@mramato I'm updating the Cesium lib on a project I inherited. In the course of this update I ran into this issue:
this.cesiumEntity.label.fillColor = Cesium.Color.BLUE;
cesiumEntity is a Cesium entity with a LabelGraphics member. In the above line of code the color is updated to a different color. This used to work in Cesium 1.55 (yeah, I know).
This line is flagged by typescript (in VSCode) as incorrect: "Type 'Color' is missing the following properties from type 'Property': ...".
But when I changed the line to:
this.cesiumEntity.label.fillColor = new Cesium.ColorMaterialProperty(Cesium.Color.BLUE);
It didn't work (ColorMaterialProperty was one of the types suggested by VSCode intellisense and judging by the name it seemed a good fit).
Next I tried changing line 21534 in node_modules/cesium/Build/Cesium/Cesium.d.ts to:
fillColor: Color | Property | undefined;
And the result was that I could assign a Color directly and it would work. This led to my assumption the problem was with the typescript definitions.
However, I can confirm that using a ConstantProperty does work, so my pull request is unnecessary.