[Wasm] Don't write .wat files in box tests

These files take space on CI, but they are not validated or processed
automatically in any way.

Disabled by default, enabled via kotlin.wasm.debugMode=1

js/js.tests/test/org/jetbrains/kotlin/js/testOld/BasicWasmBoxTest.kt

@@ -176,7 +176,7 @@ abstract class BasicWasmBoxTest(
                     println(" ------ $name Test file://$path/test.js")
                 }
 
-                writeCompilationResult(res, dir, WasmLoaderKind.D8)
+                writeCompilationResult(res, dir, WasmLoaderKind.D8, writeWat = debugMode >= DebugMode.DEBUG)
                 File(dir, "test.js").writeText(testJs)
                 ExternalTool(System.getProperty("javascript.engine.path.V8"))
                     .run(