Logcumsumexp for CPU (#93153)
Partial work from #90847, in the direction of solving #89205.
Most of the content is from #90847, but this is only for CPU, so hopefully it does not increase the build time by a lot.
tag: @albanD, @malfet
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93153
Approved by: https://github.com/malfet, https://github.com/Skylion007
