Improve documented sampling profiler steps to best known methods (#88438)

1. Add `-fdebug-info-for-profiling -funique-internal-linkage-names`,
which improve the usefulness of debug info for profiling.

2. Recommend the use of `br_inst_retired.near_taken:uppp`, which
provides the most precise results on supporting hardware. Mention
`branches:u` as a more portable backup.

Both should portray execution counts better than the default event
(`cycles`) and have a better chance of working as an unprivileged user
due to the `:u` modifier.