Inliner: add a few more observations

Inliner: add a few more observations

Now that we can trust `optMethodFlags`, note if the root caller has
newarr or newobj. We can't yet tell if these operations might feed
a particular call's arguments but their presence in the root method
alone might be enough to build correlations with performance changes.

Count number of returns in the callee. Note if callee has same this
as the (root) caller. Note when callee is a class constructor.

Add code to dump out the new observations. No policies act on these yet.

Commit migrated from https://github.com/dotnet/coreclr/commit/8c034fb97caa20f5cd824711587dcd964dae6c45