Inductor cpp wrapper: support Reduction (#88561)
For reductions, the code string in the codegen stage and the execution stage are different due to `\`.
- The code string gotten from `code.getvalue()` (`code` is an `IndentedBuffer`) in codegen stage:
```
#pragma omp declare reduction(argmax : struct IndexValue_1 :\
omp_out.value = omp_in.value < omp_out.value ? omp_out.value : omp_in.value,\
omp_out.index = omp_in.value < omp_out.value ? omp_out.index : omp_in.index)\
initializer(omp_priv = {0, -std::numeric_limits<float>::infinity()})
```
- The code string loaded during the execution (`\` will be escaped):
```
#pragma omp declare reduction(argmax : struct IndexValue_1 : omp_out.value = omp_in.value < omp_out.value ? omp_out.value : omp_in.value, omp_out.index = omp_in.value < omp_out.value ? omp_out.index : omp_in.index) initializer(omp_priv = {0, -std::numeric_limits<float>::infinity()})
```
Thus we can't get the same hash value for these two pieces of code.
This PR adds a function to make the transformation escape the backslash in the codegen stage.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88561
Approved by: https://github.com/jgong5, https://github.com/jansel, https://github.com/desertfire
