[inductor] Fix type inference in CPU masked operations (#93842)
Fixes #93351
The existing code guesses that `tmp3` is probably a `float`, and so truncates
any `double` values
```cpp
float tmp3 = 0.0;
if(tmp2)
{
auto tmp4 = in_ptr0[i0];
tmp3 = tmp4;
}
```
The proposed change is to generate a lambda expression that represents the body
of the masked operation, and infer the type from the return value:
```cpp
auto tmp3 = [&]
{
auto tmp4 = in_ptr0[i0];
return tmp4;
}
;
auto tmp5 = tmp2 ? tmp3() : static_cast<decltype(tmp3())>(0.0);
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93842
Approved by: https://github.com/jgong5, https://github.com/Valentine233, https://github.com/jansel
