Fuzzer: Remove --emit-js-shell logic and reuse fuzz_shell.js instead (#6310)

We had two JS files that could run a wasm file for fuzzing purposes:

* --emit-js-shell, which emitted a custom JS file that runs the wasm.
* scripts/fuzz_shell.js, which was a generic file that did the same.

Both of those load the wasm and then call the exports in order and print out
logging as it goes of their return values (if any), exceptions, etc. Then the
fuzzer compares that output to running the same wasm in another VM, etc. The
difference is that one was custom for the wasm file, and one was generic. Aside
from that they are similar and duplicated a bunch of code.

This PR improves things by removing 1 and using 2 in all places, that is, we
now use the generic file everywhere.

I believe we added 1 because we thought a generic file can't do all the
things we need, like know the order of exports and the types of return values,
but in practice there are ways to do those things: The exports are in fact
in the proper order (JS order of iteration is deterministic, thankfully), and
for the type we don't want to print type internals anyhow since that would
limit fuzzing --closed-world. We do need to be careful with types in JS (see
notes in the PR about the type of null) but it's not too bad. As for the types
of params, it's fine to pass in null for them all anyhow (null converts to a
number or a reference without error).

1 files changed, 2 insertions, 2 deletions

diff --git a/test/lit/exec/no-compare-refs.wast b/test/lit/exec/no-compare-refs.wast
index bfa317a53..646ec1550 100644
--- a/test/lit/exec/no-compare-refs.wast
+++ b/test/lit/exec/no-compare-refs.wast
@@ -12,11 +12,11 @@
   ;; The type of the reference this function returns will change as a result of
   ;; signature pruning. The fuzzer should not complain about this.
   ;; CHECK:      [fuzz-exec] calling return-ref
-  ;; CHECK-NEXT: [fuzz-exec] note result: return-ref => funcref
+  ;; CHECK-NEXT: [fuzz-exec] note result: return-ref => function
   (func $return-ref (export "return-ref") (result funcref)
     (ref.func $no-use-param)
   )
 )
 ;; CHECK:      [fuzz-exec] calling return-ref
-;; CHECK-NEXT: [fuzz-exec] note result: return-ref => funcref
+;; CHECK-NEXT: [fuzz-exec] note result: return-ref => function
 ;; CHECK-NEXT: [fuzz-exec] comparing return-ref