Include a simple quantization report after `QuantizeCompositeFunctionsPass`.
Include a simple quantization report after `QuantizeCompositeFunctionsPass`.

Implements a method `QuantizationReport::ToString` that returns a human-readable report that contains the textproto representation of `QuantizationResults`.
After `QuantizeCompositeFunctionsPass` it simply prints this string to stdout.

The printed report would look something like this:

```
===== Quantization Report =====

results {
  quantizable_unit {
    name: "composite_dot_general_fn_2"
  }
}
===== Quantization Report End =====
```
