Create BuilderSupplier interface

- Fixes #607

spring-shell-docs/src/main/asciidoc/using-shell-commands-programmaticmodel.adoc

@@ -12,7 +12,7 @@ include::{snippets}/CommandRegistrationBeanSnippets.java[tag=plain]
 ====
 
 If all your commands have something in common, an instance of
-a _Supplier<CommandRegistration.Builder>_ is created which can
+a _CommandRegistration.BuilderSupplier_ is created which can
 be autowired. Default implementation of this supplier returns
 a new builder so you don't need to worry about its internal state.
 

spring-shell-docs/src/test/java/org/springframework/shell/docs/CommandRegistrationBeanSnippets.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,8 +15,6 @@
  */
 package org.springframework.shell.docs;
 
-import java.util.function.Supplier;
-
 import org.springframework.context.annotation.Bean;
 import org.springframework.shell.boot.CommandRegistrationCustomizer;
 import org.springframework.shell.command.CommandRegistration;
@@ -37,7 +35,7 @@ public class CommandRegistrationBeanSnippets {
 	class Dump2 {
 		// tag::fromsupplier[]
 		@Bean
-		CommandRegistration commandRegistration(Supplier<CommandRegistration.Builder> builder) {
+		CommandRegistration commandRegistration(CommandRegistration.BuilderSupplier builder) {
 			return builder.get()
 				.command("mycommand")
 				.build();