Set SPZ Niantic Sample as reference

[CedricGuillemet]

Coordinate system used for SPZ makes Niantic samples upside down.
This PR makes SDK samples to display correctly as it uses the same coordinate system.

An option is to change your conversion code (PLY->SPZ) to flip Y,Z components of positions and orientation.
Or, use the new plugin option to do the work at runtime.

Here is an example to do the flipping when your SPZ do not use same coord system as Niantic and your scenes appear upside down:

BABYLON.LoadAssetContainerAsync("https://raw.githubusercontent.com/CedricGuillemet/dump/master/racoonfamily.spz", scene, {
    pluginOptions:{
        splat:{
           flipY: true
        }
    }
});

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

Snapshot stored with reference name:
refs/pull/16196/merge

Test environment:
https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16196/merge/index.html

To test a playground add it to the URL, for example:

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16196/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/16196/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/16196/merge
https://gui.babylonjs.com/?snapshot=refs/pull/16196/merge
https://nme.babylonjs.com/?snapshot=refs/pull/16196/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/16196/merge#BCU1XR#0

[bjsplat]

WebGL2 visualization test reporter:

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16196/merge/testResults/webgl2playwright/index.html

[bjsplat]

Visualization tests for WebGPU

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16196/merge/testResults/webgpuplaywright/index.html

[CedricGuillemet]

@ryantrem is there a way to set the loadingOptions when loading a mesh instead of using OnPluginActivatedObservable. Basically, is it possible to set flipY per import?

[bjsplat]

Visualization tests for WebGPU

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16196/merge/testResults/webgpuplaywright/index.html

[bjsplat]

WebGL2 visualization test reporter:

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16196/merge/testResults/webgl2playwright/index.html