[ExecuTorch][WebGPU] Add optimized conv2d op #11672

Job	Run time
test-vulkan / test-backend-linux (vulkan, operators) / linux-job	22m 11s
test-vulkan / test-backend-linux (vulkan, models) / linux-job	23m 44s
test-vulkan / test-backend-macos	-7s
test-vulkan / package-golden-artifacts	3m 31s
	49m 19s

Provide feedback