Fix option type parsing

- In `CommandRegistration` add `ResolvableType` for `OptionSpec` giving
  more spesific handling of a type.
- In `CommandParser` handle source and target types so that we
  have generics with `List`, `Set` and arrays working better.
- In `HandlerMethodArgumentResolver` add better handling for
  `ConversionService` for generic types.
- In `StandardMethodTargetRegistrar` add better types via `ResolvableType`
  now that `CommandRegistration` support it.
- In `OptionConversionCommands` remove converter from `String` to `Set` as
  now things should work as is if generic in a `Set` has a converter.
- Backport #694
- Fixes #699

spring-shell-samples/src/main/java/org/springframework/shell/samples/e2e/OptionConversionCommands.java

@@ -16,11 +16,12 @@
 package org.springframework.shell.samples.e2e;
 
 import java.util.Arrays;
-import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.ResolvableType;
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.shell.command.CommandRegistration;
 import org.springframework.shell.standard.ShellComponent;
@@ -54,6 +55,13 @@ public class OptionConversionCommands {
 			return "Hello " + arg1;
 		}
 
+		@ShellMethod(key = LEGACY_ANNO + "option-conversion-customlist", group = GROUP)
+		public String optionConversionCustomListAnnotation(
+			@ShellOption List<MyPojo> arg1
+		) {
+			return "Hello " + arg1;
+		}
+
 		@ShellMethod(key = LEGACY_ANNO + "option-conversion-customarray", group = GROUP)
 		public String optionConversionCustomArrayAnnotation(
 			@ShellOption MyPojo[] arg1
@@ -103,12 +111,13 @@ public class OptionConversionCommands {
 
 		@Bean
 		public CommandRegistration optionConversionCustomSetRegistration() {
-			return getBuilder()
+			ResolvableType rtype = ResolvableType.forClassWithGenerics(Set.class, MyPojo.class);
+			return CommandRegistration.builder()
 				.command(REG, "option-conversion-customset")
 				.group(GROUP)
 				.withOption()
 					.longNames("arg1")
-					.type(Set.class)
+					.type(rtype)
 					.and()
 				.withTarget()
 					.function(ctx -> {
@@ -145,11 +154,6 @@ public class OptionConversionCommands {
 		public Converter<String, MyPojo> stringToMyPojoConverter() {
 			return new StringToMyPojoConverter();
 		}
-
-		@Bean
-		public Converter<String, Set<MyPojo>> stringToMyPojoSetConverter() {
-			return new StringToMyPojoSetConverter();
-		}
 	}
 
 	public static class MyPojo {
@@ -180,14 +184,4 @@ public class OptionConversionCommands {
 			return new MyPojo(from);
 		}
 	}
-
-	static class StringToMyPojoSetConverter implements Converter<String, Set<MyPojo>> {
-
-		@Override
-		public Set<MyPojo> convert(String from) {
-			Set<MyPojo> set = new HashSet<>();
-			set.add(new MyPojo(from));
-			return set;
-		}
-	}
 }