Extract U32 texture data upload logic and restore pixelStorei parameters

[mrxz]

Both SplatPager and SparkRenderer manually uploaded texture data using the WebGLRenderingContext directly. This stems from a limitation in Three.js preventing 2D regions from easily being updated, see mrdoob/three.js#32254. This PR extracts the logic into a utility function to avoid duplication.

Additionally the pixelStorei parameters set as part of this procedure weren't restored to the values they were before the upload. This becomes a problem with Three.js >= r184 as it now caches the parameter values in its WebGLState, see #366. This PR ensures they are now properly restored. Once Spark requires Three.js 184 or later it can switch to renderer.state.pixelStorei instead.

Fixes #366

[dmarcos]

we should probably bump to r184 sooner than later

[mrxz]

we should probably bump to r184 sooner than later

On one hand keeping up with the latest release is nice to ensure it keeps working, but we should stick to the oldest version we intend to support. Especially considering not all frameworks that use Three.js update at the same cadence as Three itself. Unless there is a clear reason for it, Spark shouldn't force users to update Three IMHO.

It's unfortunate when things break/regress like it did here, but that's likely going to be infrequent, whereas building against/relying on new additions/features is a bigger compat risk.