Updating pull request process and guidelines

Hello all! We are working on some updates to our pull request process, and this will impact community pull requests. As part of it we are going to update our contribution guidelines a bit, but we wanted to give you as much notice as we could through a pinned issue.
1) We are going to add some automation so that PRs that have been in draft state for a significant period of time will be automatically closed. This helps us focus on the PRs that are more active/more actively maintained/have recently gotten an update. As a contributor, should you wish to reopen the PR, you are welcome to do so; this sends a signal that fixing the particular issue remains of interest to you.
2) We are going to add some automation so that PRs that are active and haven't been modified for a significant period of time are converted to draft (which becomes the last edit for the "1" above). This helps us focus on the PRs that are more active/more actively maintained/have recently gotten an update. As a contributor, should you wish to re-publish the PR, you are welcome to do so; this sends a signal that fixing the particular issue remains of interest to you.
3) For changes related to performance of specific parts of the Roslyn code base, we are going to ask that you have a benchmark available that we can run; this is in support of a measure-change-measure pattern of performance improvements.

We absolutely want community contributions, and by making these changes we should be able to focus time on helping those great contributions get into the product.

Start by reviewing the pinned issue's three planned changes to the pull request process and the repository's contribution guidelines. The issue does not name files, tests, or entry points. Done would require the updated guidelines and planned automation to reflect the stated draft, inactivity, and performance-benchmark policies.

Written by the indexing model from the issue text.