weight pre-packing ops.


ReLU/Hardtanh fusion: XNNPACK ops support fusion of clamping.
     That is clamping of output activation is done as part of the
     kernel, including for 2D convolution and linear op kernels. Thus
     clamping effectively comes for free. Thus any op that can be
     expressed as clamping op, such as "ReLU" or "hardtanh", can be
     fused with previous "Conv2D" or "linear" op in XNNPACK. This pass
     rewrites graph by finding "ReLU/hardtanh" ops that follow XNNPACK
     "Conv2D/linear" ops, written by the previous pass, and fuses them
     together.


Dropout removal (blocklisting option
     mobile_optimizer.MobileOptimizerType.REMOVE_DROPOUT): This
     optimization pass removes "dropout" and "dropout_" nodes from
     this module when training is false.


Conv packed params hoisting (blocklisting option
     mobile_optimizer.MobileOptimizerType.HOIST_CONV_PACKED_PARAMS):
     This optimization pass moves convolution packed params to the

