Log event for slow glob evaluation so VS can alert users

We've seen several reports from customers where glob evaluation has severely affected VS performance:

1. One customer with ~600 projects and ~200,000 files had a glob in a targets file imported by all projects that looked for files from the root, accounting for 6s out of a total of 8s of evaluation time while loading the solution.
2. It's not uncommon for internal customers to have globs that are rooted by an env var - then when they open in VS without that env var set, the evaluation end up being rooted at `\` and takes forever.

We discussed mitigations for this, and it would be nice if MSBuild could log an event once evaluation has takes more than a certain threshold (ideally including which glob it was and where it was rooted). Then VS could hook that up to a perf tip.