[WebGPU EP] adjusts pow op to use sqrt when exponent is 0.5

[prathikr]

Resolves the below error for florence2 model by using WebGPU built-in sqrt(x) function instead of pow(x, y) when the exponent is 0.5. The sqrt(x) built-in is both faster and more stable than using pow(x, 0.5).

Non-zero status code returned while running Reshape node. Name:'/Reshape_1' Status 
Message: /Users/runner/work/1/s/onnxruntime/core/providers/cpu/tensor/reshape_helper.h:47 
  onnxruntime::ReshapeHelper::ReshapeHelper(const TensorShape &, TensorShapeVector &, bool) input_shape_size == size was false. 
  The input tensor cannot be reshaped to the requested shape. Input shape:{1,576,32}, requested shape:{1,23,23,32}

[fs-eire]

please add a new unittest for the fix