[C# 10 diagnostics] - Misc items #51450
Description
Describe the issue or suggestion
Add the following:
- CS8918 pattern matching
- CS8935 - async method builder
- CS8940 - async method builder
- CS8937 - top level statements
- CS8973 - checked overflow
top level statements, and checked overflow may involve consolidation with many existing articles, and therefore may be independent PRs