Handle metadata annotations in parameter lists with trailing commas.

test/whitespace/metadata.unit

 40 columns                              |
 >>> force newline before directives
 @deprecated library foo;
 
 @deprecated import 'dart:io';
 
 @deprecated export 'dart:io';
 <<<
 @deprecated
 library foo;
@@ skipping 191 matching lines @@
     @foo @bar int fn(@foo param)) {}
 withoutReturnType(
     @foo @bar fn(@foo param)) {}
 >>> metadata on default formal parameter
 positional([@foo bar]) {}
 named({@foo bar}) {}
 <<<
 positional([@foo bar]) {}
 named({@foo bar}) {}
 >>> split between metadata and parameter indents
-function(@VeryLongMetadataAnnotation longParameter) {}
+function(@Annotation @VeryLongMetadataAnnotation longParameter) {}
 <<<
 function(
+    @Annotation
     @VeryLongMetadataAnnotation
-        longParameter) {}
+        longParameter) {}
+>>> unsplit with trailing commas
+function(@Annotation longParameter,@Annotation @Other longParameter2,) {}
+<<<
+function(
+  @Annotation longParameter,
+  @Annotation @Other longParameter2,
+) {}
+>>> split with trailing commas
+function(@Annotation longParameter,@Annotation @Other @Third longParameter2,) {}
+<<<
+function(
+  @Annotation longParameter,
+  @Annotation
+  @Other
+  @Third
+      longParameter2,
+) {}