[llvm] [llvm-profgen] Add --sample-period to estimate absolute counts (PR #99826)

[Tim Creech via llvm-commits]

tcreech-intel wrote:

@williamweixiao, @HaohaiWen, it may also be useful to have this PR, which adds `--sample-period` functionality. This is a nice usability improvement.
(It's a separate PR because it depends on the changes in #99026.)

https://github.com/llvm/llvm-project/pull/99826