Calculate quantized convolution multiplier using double type.

NNAPI has been using the float type for quantized convolution multiplier
calculation, which was causing an occasional off-by-one differences for
convolution operation results between TFLite/CPU and NNAPI/CPU implementations.

Test: MLTS com.android.nn.benchmark.app.NNTest#testNNAPI[mobilenet_*_quant] error rates
Test: NeuralNetworksTest_static
Bug: 115377572
Change-Id: If0bb9ff7229f5b3864a69c66566a4e4008f94c37