Some refactoring of the fakes package (Azure#20831)

* Some refactoring of the fakes package

Deeper testing uncovered some deficiencies as well as general API
improvements like slight renaming and adding options types.
Marshalling APIs (used by fake server) now take an any type instead of a
Responder[T] in order to handle cases where we marshal from a scalar.
Added support for binary, text, and XML formats (binary was halfway
there already, supporting form and multipart but not vanilla).
Added support for specifying an HTTP status code in a fake response.
Added and cleaned up various doc comments.

* fix doc comment

* MarshalResponseAsText takes param by pointer

* remove empty string from MarshalResponseAsText

* renamed AddNonTerminalError to AddPollingError to clarify its behavior

removed HTTP status values from SetReponseOptions as this will be
handled by the generated fake servers.
don't panic on nil request bodies.

* add support for byte arrays

* merge NewBinaryResponse into NewResponse with optional body params

sdk/azcore/fake/example_test.go

@@ -50,9 +50,9 @@ func ExampleResponder() {
 	resp := fake.Responder[WidgetResponse]{}
 
 	// here we set the instance of Widget the Responder is to return
-	resp.Set(WidgetResponse{
+	resp.SetResponse(WidgetResponse{
 		Widget{ID: 123, Shape: "triangle"},
-	})
+	}, nil)
 
 	// optional HTTP headers can also be included in the raw response
 	resp.SetHeader("custom-header1", "value1")
@@ -119,7 +119,7 @@ func ExamplePollerResponder() {
 
 	// non-terminal errors can also be included in the sequence of responses.
 	// use this to simulate an error during polling.
-	pollerResp.AddNonTerminalError(errors.New("flaky network"))
+	pollerResp.AddPollingError(errors.New("flaky network"))
 
 	// use SetTerminalResponse to successfully terminate the long-running operation.
 	// the provided value will be returned as the terminal response.
@@ -128,7 +128,7 @@ func ExamplePollerResponder() {
 			ID:    987,
 			Shape: "dodecahedron",
 		},
-	})
+	}, nil)
 }
 
 func ExamplePollerResponder_SetTerminalError() {