KTX2Loader: Add WebGPU support.

[Mugen87]

Related issue: #25864, #25865

Description

This PR ensures KTX2Loader can also detect support with WebGPURenderer.

There is one issue that needs to be discussed: KTX2Loader.detectSupport() requires the renderer to test for compressed texture formats. This test requires the WebGPU adapter which is only available when the init() routine of WebGPURenderer has been finished. The changes to webgpu_sandbox shows the consequences on app level.

This also means if you would exchange WebGLRenderer with WebGPURenderer in an application that uses KTX2Loader, the app has to use the async/await pattern. I'm not sure right now if there is another way to test GPU features in WebGPU without async code (because you need the adapter for this and you only get it async).

[Mugen87]

This is also something that might cause troubles. You have to specify the required features (e.g. texture compression formats) when WebGPURenderer is created.

That means a viewer application would have to know in advance what type of assets are going to be imported so it can request the respective features (which is of course unrealistic). I wonder now if it's best to always request all supported features (that includes texture compression formats) every time WebGPURenderer is created. Something like the following in WebGPURenderer.init():

const gpuAdapter = await navigator.gpu.requestAdapter();

const features = [];

for ( const name of featureNames ) {

    if ( gpuAdapter.features.has( name ) ) {

        features.push( name );

    }

}

const deviceDescriptor = {
    requiredFeatures: features
};

const device = await adapter.requestDevice( deviceDescriptor );