[FEATURE SUGGESTION] Consider setting alphaDepthMask to false by default for transparent objects

[xeolabs]

Consider setting alphaDepthMask to false by default for transparent objects.

When alphaDepthMask is true, we see the transparent windows in the foreground preventing the windows in the background from rendering, because the close windows happen to render before the far windows in the display list, and Z-reject prevents the latter from being drawn.

    const viewer = new Viewer({
        canvasId: "myCanvas",
        transparent: false,
        alphaDepthMask: true
    });

With alphaDepthMask false, we see both the windows in forgeround and background, because this prevents Z-reject between them, and they both blend with each other into the color buffer.

const viewer = new Viewer({
        canvasId: "myCanvas",
        transparent: false,
        alphaDepthMask: false
    });

Also consider setting the Viewer's transparent configuration to false by default. This refers to indicating that the HTML Canvas element is transparent. Transparent object blending looks washed out when 'transparent' is true, and users may never realize that transparent object blending looks much better when 'transparent' configuration is `false'.