Fix tests, add depth_multiplier value check in DEPTHWISE_CONV_2D.

depth_multiplier value was not validated in the
depthwiseConvPrepare method. Newly added tests for the per-channel
quantized convolution had wrong output channel count for their
depth_multiplier value, which was not checked.

+ Minor fix in CpuExecutor, removed use of a filter mOperand field

Bug: 122046844
Test: NeuralNetworksTest_static
Change-Id: I95a187c48dcdb5a8c831557aac35da884680e2c0