[JS IR BE] Fix main function detector

- Do not consider extension functions as main candidate

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/utils/JsMainFunctionDetector.kt

@@ -26,6 +26,7 @@ object JsMainFunctionDetector {
         if (!isSuitableForMainParametersSize(allowEmptyParameters)) return false
         if (!returnType.isUnit()) return false
         if (name.asString() != "main") return false
+        if (extensionReceiverParameter != null) return false
 
         if (valueParameters.size == 1) {
             val parameter = valueParameters.single()

js/js.translator/testData/box/main/differentMains.kt

@@ -20,4 +20,8 @@ fun main(args: Array<String>): Unit? {
     return Unit
 }
 
+fun Any.main(args: Array<String>) {
+    ok += "Fail Any.main(...)"
+}
+
 fun box() = ok