[llvm-profgen] Add an option to mark all the profile context as preinlined (#156501)
Add a new option (under `--mark-all-context-preinlined`) that marks all
function samples with the `ContextShouldBeInlined ` attribute during
post-processing to make the profile as preinlined. This can be useful
for experiments outside of the CS preinliner, e.g. to fully replay the
inlining for a given profile.