Use Array.Empty for parameterless filters

[captainsafia]

Closes #41705

Validation

app.MapGet("/", () => "Look ma! No params.")
    .AddFilter((c, n) => n(c));

> 1..1000 | % { curl http://localhost:5000 }

Before Change

Type	Allocations
+ System.Object[]	1,698
| - System.Object[0]	1,003

After Change

Type	Allocations
+ System.Object[]	702
| - System.Object[0]	2

[BrennanConroy]

Shouldn't MakeGenericMethod be hoisted to the stored MethodInfo so we use the same one for every filter factory?

[davidfowl]

Can cache this one for object too since we're not using the open generic to close over other arrays yes.