[EH][test] Split EH tests into old and new spec (WebAssembly#6178)

This moves tests for the old EH spec to `exception-handling-old.wast`
and moves the new `exnref` test into `exception-handling.wast`, onto
which I plan to add more tests for the new EH spec.

The primary reason for splitting the files is I plan to exclude the new
EH test from the fuzzing while the new spec's implementation is in
progress, and I don't want to exclude the old EH tests altogether.

Author: aheejin

scripts/fuzz_opt.py

@@ -315,6 +315,8 @@ def is_git_repo():
     'multi-memory-lowering-import-error.wast',
     # the fuzzer does not support typed continuations
     'typed_continuations.wast',
+    # New EH implementation is in progress
+    'exception-handling.wast',
 ]