The number of mipmap levels in this GraphicsTexture.
The value includes the base level, so it must always be 1 or more.
Note that a GraphicsTexture represents what is uploaded to the GPU, so this value may differ from Texture.mipmapCount depending on the values of Texture2D.activeMipmapLimit and Texture2D.streamingMipmaps.
If the GraphicsTextureDescriptor.format is a depth-only format, then mipCount is ignored.