[FEAT] Remove unnecessary data copying in WebGPU.

[Sh-Zh-7]

For convenience, current implementation of WebGPU backend copys data every time when executing a operator.
HPC is all about data movement. It's hard to imagine how much time we spent on these useless data movement.
Consider replace data field with WebGPU buffer type member in WebGPU tensor definition.
And computePass() function should be modified as well, never copy back result back in its end.