Fixed visibility of 4.2's additional default converters

Issue: SPR-12175
Issue: SPR-13020

spring-core/src/main/java/org/springframework/core/convert/support/StreamConverter.java

@@ -36,7 +36,7 @@ import org.springframework.lang.UsesJava8;
  * @since 4.2
  */
 @UsesJava8
-public class StreamConverter implements ConditionalGenericConverter {
+class StreamConverter implements ConditionalGenericConverter {
 
 	private static final TypeDescriptor STREAM_TYPE = TypeDescriptor.valueOf(Stream.class);
 
@@ -107,8 +107,7 @@ public class StreamConverter implements ConditionalGenericConverter {
 	}
 
 	private Object convertToStream(Object source, TypeDescriptor sourceType, TypeDescriptor streamType) {
-		TypeDescriptor targetCollection =
+		TypeDescriptor targetCollection = TypeDescriptor.collection(List.class, streamType.getElementTypeDescriptor());
-				TypeDescriptor.collection(List.class, streamType.getElementTypeDescriptor());
 		List<?> target = (List<?>) this.conversionService.convert(source, sourceType, targetCollection);
 		return target.stream();
 	}

spring-core/src/main/java/org/springframework/core/convert/support/StringToCharsetConverter.java

@@ -26,7 +26,7 @@ import org.springframework.core.convert.converter.Converter;
  * @author Stephane Nicoll
  * @since 4.2
  */
-public class StringToCharsetConverter implements Converter<String, Charset> {
+class StringToCharsetConverter implements Converter<String, Charset> {
 
 	@Override
 	public Charset convert(String source) {