Avoid reporting VSTHRD200 violation for async Main method when using System.CommandLine.DragonFruit

Is your feature request related to a problem? Please describe.

When using System.CommandLine.DragonFruit, a violation of VSTHRD200 is currently reported for an async Task Main(...) method with named arguments. This appears to be due to the fact that this form of Main method is not identified as the entry point in the semantic model compilation, but instead is identified via System.CommandLine.DragonFruit.EntryPointDiscoverer.

Describe the solution you'd like

It would be convenient if a DragonFruit-style async Main method did not trigger VSTHRD200. This could be accomplished by using the EntryPointDiscoverer to try to identify the entry point if one is not found using the semantic model and System.CommandLine is referenced.

Describe alternatives you've considered

It's obviously feasible to suppress a violation of the rule as a false positive. However, this is equally true for a "standard" async Main method, and addressing that one (#187) appears to have been deemed worthwhile.

Additional context

n/a

Start by reviewing System.CommandLine.DragonFruit.EntryPointDiscoverer.cs and the analyzer's semantic-model entry-point lookup. Done means a DragonFruit-style async Task Main method with named arguments no longer reports VSTHRD200 when System.CommandLine is referenced, while standard entry-point behavior remains covered.