Describe the solution you'd like

Like we built for Go and built for Java, there is a desire for a "workflow check" analyzer for .NET.

Initial notes/thoughts:

• Should be a diagnostic/Roslyn analyzer called "workflow check" to match Go and Java equivalents
• Should transitively check known-yet-configurable invalid actions occurring in a workflow
  • Transitive is the key/hard part
    • This requires coloring methods as "Temporal invalid" or not, and any method that invokes an invalid method is itself invalid, so this is basically call graph building
    • For Go, diagnostic checks support "facts" which are effectively serializable metadata that can be attached to typed AST, so that was used to mark a method as invalid (including transitively)
    • For Java, no such thing exists, so we had to completely write an analyzer from scratch
    • Like Java, .NET analyzer can ideally work from workflow method out and not have to eagerly color all methods
    • The error needs to show the call graph stack since many times the issue is several calls deep from the workflow itself
  • Understood that this will miss some things, e.g. reflection
  • See https://github.com/temporalio/sdk-dotnet#workflow-logic-constraints and https://github.com/temporalio/sdk-dotnet?tab=readme-ov-file#net-task-determinism for what constitutes an invalid action
• Ideally, should disable or invert certain existing analyzer/diagnostic warnings that are not applicable to workflows
  • See https://github.com/temporalio/sdk-dotnet?tab=readme-ov-file#workflow-editorconfig for set of rules that should be inverted/disabled
• If analyzer is cheap enough performance-wise to enable by default when using the Temporalio NuGet package, should do so
• Ideally, if the rules are not too granular, we can create entries at https://github.com/temporalio/rules for each one (so we should prefix with TMPRL)
  • Even if they are fairly granular, it is something we may want
• https://learn.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-roslyn-analyzer already exists for those curious

Admittedly research has not been done to confirm that all of these features are possible with .NET code analyzers.