CA2016 - Flag cases where called methods accept a CancellationToken

[MattKotsenas]

Analyzer

Diagnostic ID: CA2016

Describe the improvement

Currently rule CA2016 appears to be limited to cases where the containing method has a CancellationToken as a parameter. However, there are cases where a CancellationToken is available some other way (i.e. code analyzer's AnalysisContext).

It's also a signal to refactor when code is calling methods that take CancellationTokens but no token is available.

Describe suggestions on how to achieve the rule

Here's a good blog post that shows additional cases that can be caught: https://www.meziantou.net/detect-missing-cancellationtoken-using-a-roslyn-analyzer.htm

Additional context

I'm happy to take a first pass at this, but wanted to make sure this wasn't already considered and rejected.

[sharwell]

Related issues in the past:

DotNetAnalyzers/AsyncUsageAnalyzers#36
DotNetAnalyzers/AsyncUsageAnalyzers#37
DotNetAnalyzers/AsyncUsageAnalyzers#43