Change return of SkipPastLikelyEnd to be last consumed token (#3493)

This approach means the parse subtree includes the full token range
consumed.

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

toolchain/parse/handle_decl_scope_loop.cpp

@@ -52,19 +52,12 @@ static auto TryHandleEndOrPackagingDecl(Context& context) -> bool {
 static auto FinishAndSkipInvalidDecl(Context& context, int32_t subtree_start)
     -> void {
   auto cursor = *context.position();
-  // Consume to the next `;` or end of line. We ignore the return value since
-  // we only care how much was consumed, not whether it ended with a `;`.
-  // TODO: adjust the return of SkipPastLikelyEnd or create a new function
-  // to avoid going through these hoops.
-  context.SkipPastLikelyEnd(cursor);
-  // Set `iter` to the last token consumed, one before the current position.
-  auto iter = context.position();
-  --iter;
-  // Output an invalid parse subtree including everything up to the last token
-  // consumed.
+  // Output an invalid parse subtree including everything up to the next `;`
+  // or end of line.
   context.ReplacePlaceholderNode(subtree_start, NodeKind::InvalidParseStart,
                                  cursor, /*has_error=*/true);
-  context.AddNode(NodeKind::InvalidParseSubtree, *iter, subtree_start,
+  context.AddNode(NodeKind::InvalidParseSubtree,
+                  context.SkipPastLikelyEnd(cursor), subtree_start,
                   /*has_error=*/true);
 }