[JimBobSquarePants]

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Description

Adds the missing Bgra32 constructors to match Rgba32, Argb32, and Abgr32:

• A packed uint value.
• Normalized float RGB components, with optional alpha.
• A Vector3, with opaque alpha.
• A Vector4.

The packed constructor copies the stored BGRA bits without color conversion. Its documentation explains memory order and the little-endian 0xAARRGGBB integer layout. The float and vector constructors reuse the existing packer.

Extends Bgra32Tests to check packed bits, channel order, normalized component conversion, bounds, and implicit opaque alpha.

Release validation on .NET 8: all 25 Bgra32Tests pass.

Addresses the constructor gap identified in discussion #3184.