[llvm] Make llvm::telemetry::Manager::preDispatch protected. (PR #127114)

[Pavel Labath via llvm-commits]

labath wrote:

> (@jh7370 FYI)
> 
> LGTM.
> 
> This is definitely less important, but I'm also wondering if there's a reason for `dispatch` to be virtual (given that `preDispatch` is sort of the official customization point for messing with entries).

Okay, I've read https://github.com/llvm/llvm-project/pull/126588#discussion_r1955094168 now. I can live with that, though I don't find that example particularly compelling as parallelism could be achieved by handing the telemetry entry to a different thread from inside Destination::receiveEntry (which is also virtual).

https://github.com/llvm/llvm-project/pull/127114