Create IResult-returning static methods

[halter73]

IResult-returning static methods would allow something like using static Microsoft.AspNetCore.Http.Results and makes for better return type inference for IResult-returning lambdas, so you don't have to do casting like the following you have to do using constructors today.

app.MapGet("/todos/{id}", async (int id) =>
{
    using var db = new TodoDbContext(options);
 
    if (await db.Todos.FindAsync(id) is not Todo todo)
    {
        return (IResult)new NotFoundResult();
    }
 
    return new JsonResult(todo);
})

With, IResult returning NotFound and Ok methods the (IResult) casting can be removed.

app.MapGet("/todos/{id}", async (int id) =>
{
    using var db = new TodoDbContext(options);
 
    if (await db.Todos.FindAsync(id) is not Todo todo)
    {
        return NotFound();
    }
 
    return Json(todo);
})

[davidfowl]

We should start with these methods and remove a bunch:

https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc.controllerbase?view=aspnetcore-5.0

cc @pranavkm

[davidfowl]

@pranavkm StatusCodeResult still implements IResult. Is that intentional?