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 #699
- Fixes #700

spring-shell-standard/src/main/java/org/springframework/shell/standard/StandardMethodTargetRegistrar.java

@@ -16,6 +16,7 @@
 package org.springframework.shell.standard;
 
 import java.lang.reflect.Method;
+import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -146,8 +147,9 @@ public class StandardMethodTargetRegistrar implements MethodTargetRegistrar {
 						if (!longNames.isEmpty() || !shortNames.isEmpty()) {
 							log.debug("Registering longNames='{}' shortNames='{}'", longNames, shortNames);
 							Class<?> parameterType = mp.getParameterType();
+							Type genericParameterType = mp.getGenericParameterType();
 							OptionSpec optionSpec = builder.withOption()
-								.type(parameterType)
+								.type(genericParameterType)
 								.longNames(longNames.toArray(new String[0]))
 								.shortNames(shortNames.toArray(new Character[0]))
 								.position(mp.getParameterIndex())