Allow to specify scalars data type?

[FezVrasta]

As part of some performance optimizations work we are doing, we noticed that a huge bottleneck is located at the vtk.js updateArrayDataType helper (of Rendering/OpenGL/Texture).

The issue is that image.getPointData().getScalars() can return any kind of typed array, while the webgl logic requires a Float32Array. Any time vtk needs to render something, it needs to convert the scalars to the expected format, and this produces many garbage collection events and general slowness due to the size of the scalars data.

If itk-wasm provided an option to pre-convert the scalars in the Float32Array type, we could avoid all the above.

Do you think this is something that you could add to this lib?