[WebNN EP] Deprecate MLTensorUsage in favor of boolean flags

[huningxin]

This is changed by Chromium CL: https://chromium-review.googlesource.com/c/chromium/src/+/5933323

dictionary MLTensorDescriptor : MLOperandDescriptor {
  boolean importableToWebGPU = false;
  boolean readable = false;
  boolean writable = false;

  // TODO(crbug.com/343638938): Remove this after the M132 branch cut.
  MLTensorUsageFlags usage;
};

/cc @Honry @egalli @fdwr