Support late bound results

[davidfowl]

• Add support for object, Task<object> and ValueTask<object> result types. We can detect that pattern and generate calls into a helper that does a bunch of runtime checks for known result types.
• We don't support Task<?> or ValueTask<?>. the result will be a JSON serialized Task<T> and ValueTask<T>
• Added tests

Fixes #34247

[halter73]

Might as well remove the // TODO: Handle custom awaitables comment 😄

[halter73]

Should we treat object return values as void response types in the EndpointMetadataApiDescriptionProvider now?

aspnetcore/src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

Lines 237 to 241 in 12c57a5

	// Can't determine anything about IResults yet that's not from extra metadata. IResult<T> could help here.
	if (typeof(IResult).IsAssignableFrom(responseType))
	{
	responseType = typeof(void);
	}

[davidfowl]

Should we treat object return values as void response types in the EndpointMetadataApiDescriptionProvider now?

Yes

[davidfowl]

Though I wonder what happens if you leave it as object. I'll check.

[davidfowl]

Might as well remove the // TODO: Handle custom awaitables comment 😄

We still need to do this for F#