Fix undefined behavior in QuantizedConv2D

Added more input validation and tests.  Prior to this, we could get
`nullptr` exceptions when attempting to access 0th elements of 0-sized
inputs, leading to security vulnerability bugs.

Also needed to modify `quantized_conv_ops_test.cc` for consistency.
Previously the CPU kernel did technically support passing tensors
of rank larger than 0 for min/max values.  However, the XLA kernels do not.

PiperOrigin-RevId: 445518507