Add XML documentation to named Color properties in Android.Graphics.Color

[Copilot]

The 141 predefined named Color static properties (Transparent through YellowGreen) in Android.Graphics.Color had no /// XML doc comments, leaving developers with no IntelliSense summaries and triggering CS1591 for undocumented public members.

Changes

• Added a one-line <summary> to every named-color static property in the block, referencing the ARGB hex value from the property body and a lowercase color name description
• Transparent gets a distinct summary noting full transparency; its ARGB is documented as #00000000 to make the zero alpha channel explicit
• No runtime values or behavior changed

/// <summary>Gets a fully transparent <see cref="Color" /> (ARGB #00000000).</summary>
public static Color Transparent { get { return new Color (0x000000); } }

/// <summary>Gets a <see cref="Color" /> with the ARGB value #FFEE82EE (violet).</summary>
public static Color Violet { get { return new Color (0xFFEE82EE); } }