[Parser] Allow any number of foldedinsts in `foldedinsts` (#5965)

Somewhat counterintuitively, the text syntax for a folded `if` allows any number
of folded instructions in the condition position, not just one. Update the
corresponding `foldedinsts` parsing function to parse arbitrary sequences of
folded instructions and add a test.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/parser/input.h b/src/parser/input.h
index 5c7c57d20..5cb2bd471 100644
--- a/src/parser/input.h
+++ b/src/parser/input.h
@@ -62,6 +62,7 @@ struct ParseInput {
   std::optional<std::string_view> takeString();
   std::optional<Name> takeName();
   bool takeSExprStart(std::string_view expected);
+  bool peekSExprStart(std::string_view expected);
 
   Index getPos();
   [[nodiscard]] Err err(Index pos, std::string reason);