Remove bean cycles

- Shuffle things around into different auto-config and configuration
  classes and use other tricks like ObjectProvider to work around
  boot 2.6.x imposing bean cycle checks.
- This is first set of changes to work around this issue, not
  to make things perfect. Further refactoring work is needed
  making code base more boot 2.x friendly as things are based
  on boot 1.5.x times.
- Fixes #324

spring-shell-test-samples/src/test/java/com/example/test/integration/CalculatorCommandsIntegrationTest.java

@@ -8,6 +8,7 @@ import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.shell.CommandRegistry;
 import org.springframework.shell.MethodTarget;
 import org.springframework.shell.Shell;
 import org.springframework.shell.jline.InteractiveShellApplicationRunner;
@@ -23,8 +24,7 @@ import static org.springframework.util.ReflectionUtils.findMethod;
  *
  * @author Sualeh Fatehi
  */
-@SpringBootTest(properties = { InteractiveShellApplicationRunner.SPRING_SHELL_INTERACTIVE_ENABLED + "=" + false,
-		"spring.main.allow-circular-references=true" })
+@SpringBootTest(properties = { InteractiveShellApplicationRunner.SPRING_SHELL_INTERACTIVE_ENABLED + "=" + false })
 @ContextConfiguration(classes = TestCalculatorStateConfig.class)
 public class CalculatorCommandsIntegrationTest extends BaseCalculatorTest {
 
@@ -33,6 +33,9 @@ public class CalculatorCommandsIntegrationTest extends BaseCalculatorTest {
 	@Autowired
 	private Shell shell;
 
+	@Autowired
+	private CommandRegistry commandRegistry;
+
 	@Autowired
 	private CalculatorState state;
 
@@ -45,7 +48,7 @@ public class CalculatorCommandsIntegrationTest extends BaseCalculatorTest {
 		final String command = "add";
 		final String commandMethod = "add";
 
-		final MethodTarget commandTarget = lookupCommand(shell, command);
+		final MethodTarget commandTarget = lookupCommand(commandRegistry, command);
 		assertThat(commandTarget).isNotNull();
 		assertThat(commandTarget.getGroup()).isEqualTo("Calculator Commands");
 		assertThat(commandTarget.getHelp()).isEqualTo("Add two integers");
@@ -67,7 +70,7 @@ public class CalculatorCommandsIntegrationTest extends BaseCalculatorTest {
 		final String command = "add-to-memory";
 		final String commandMethod = "addToMemory";
 
-		final MethodTarget commandTarget = lookupCommand(shell, command);
+		final MethodTarget commandTarget = lookupCommand(commandRegistry, command);
 		assertThat(commandTarget).isNotNull();
 		assertThat(commandTarget.getGroup()).isEqualTo("Calculator Commands");
 		assertThat(commandTarget.getHelp()).isEqualTo("Add an integer to the value in memory");