[webgpu]Add MaxPool and AveragePool (#23714)
This adds Max and Average pool operators for webgpu-native. Basically,
this is a rewrite of the corresponding JSEP operators with some
improvements:
1) 'dilations' support
2) Pooling with kernelShape.length > 2 for NHWC format
3) code cleanup
However, there are still a few missing features:
1) ceil 'ceil_mode'
2) column major 'storage_order'
3) 'Indices' output for Max pools.
