[wasm] Pass --experimental-wasm-exnref to V8 for perf runs (#5247)

The runtime switched WASM exception handling to the standardized exnref
proposal (dotnet/runtime#129851), which V8 keeps behind the
--experimental-wasm-exnref flag. The perf wasm v8 leg installs V8 via jsvu
and runs benchmarks through BenchmarkDotNet, which was not passing the flag,
so MicroBenchmarks aborts at startup with 'This browser/engine doesn't
support WASM exception handling' / 'Top-level await promise never resolved'.

Pass the flag through BDN's --wasmArgs for the v8 engine on both the wasm and
wasm_coreclr legs. Gated on v8 so JavaScriptCore is unaffected; harmless
(warning only) on V8 builds that enable exnref by default.

See dotnet/runtime#129849.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: DrewScoggins

scripts/run_performance_job.py

@@ -443,6 +443,12 @@ def get_bdn_arguments(
             "--wasmProcessTimeout", "20",
         ]
 
+        # The runtime now uses the standardized exnref WASM exception-handling proposal,
+        # which V8 keeps behind --experimental-wasm-exnref. Pass it through to the engine
+        # via BDN's --wasmArgs (the escaped quotes keep it a single token on the Helix shell).
+        if javascript_engine == "v8":
+            bdn_arguments += ["\\\"--wasmArgs=--experimental-wasm-exnref\\\""]
+
         if is_aot:
             bdn_arguments += [
                 "--aotcompilermode", "wasm",
@@ -460,6 +466,12 @@ def get_bdn_arguments(
             "--wasmProcessTimeout", "20"
         ]
 
+        # The runtime now uses the standardized exnref WASM exception-handling proposal,
+        # which V8 keeps behind --experimental-wasm-exnref. Pass it through to the engine
+        # via BDN's --wasmArgs (the escaped quotes keep it a single token on the Helix shell).
+        if javascript_engine == "v8":
+            bdn_arguments += ["\\\"--wasmArgs=--experimental-wasm-exnref\\\""]
+
     if runtime_type == "coreclr_r2r_interpreter":
         if os_group == "windows":
             bdn_arguments += [