Add conditionalGroup to allow manually specifying multiple representations of a document; use it to support expanding last parameter of functions

tests/node_tests/buffer/__snapshots__/jsfmt.spec.js.snap

@@ -103,18 +103,18 @@ buffer = buffer.fill(\"a\", 0, 0, \"utf8\");
 
 buffer = buffer.fill(\"a\", \"utf8\");
 
-maybeNum = buffer.find(
-  (element: number, index: number, array: Uint8Array) => false
-);
+maybeNum = buffer.find(, (element: number,
+index: number,
+array: Uint8Array) => false);
 
 maybeNum = buffer.find(
   (element: number, index: number, array: Uint8Array) => false,
   buffer
 );
 
-num = buffer.findIndex(
-  (element: number, index: number, array: Uint8Array) => false
-);
+num = buffer.findIndex(, (element: number,
+index: number,
+array: Uint8Array) => false);
 
 num = buffer.findIndex(
   (element: number, index: number, array: Uint8Array) => false,