[Wasm GC] Automatically make RefCast heap types more precise (#5704)

We already did this for nullablilty, and so for the same reasons we should do it
for heap types as well. Also, I realized that doing so would solve #5703, which
is the new test added for TypeRefining here.

The fuzz bug solved here is that our analysis of struct gets/sets will skip
copy operations - a read from a field that is written into it. And we skip
fallthrough values while doing so, since it doesn't matter if the read goes
through an if arm or a cast. An if would automatically get a more precise
type during refinalize, so this PR does the same for a cast basically.

Fixes #5703

1 files changed, 1 insertions, 1 deletions

diff --git a/test/heap-types.wast.fromBinary b/test/heap-types.wast.fromBinary
index e69cf99b1..99637f92b 100644
--- a/test/heap-types.wast.fromBinary
+++ b/test/heap-types.wast.fromBinary
@@ -324,7 +324,7 @@
    )
   )
   (drop
-   (ref.cast null $struct.B
+   (ref.cast null none
     (ref.null none)
    )
   )