[Wasm] Stop supporting "_export.js" in test infra, use import/export capability in relevant tests

* It works slightly differently in SpiderMonkey.
* It was a hack.

wasm/wasm.tests/test/org/jetbrains/kotlin/wasm/test/BasicWasmBoxTest.kt

@@ -68,8 +68,7 @@ abstract class BasicWasmBoxTest(
             val languageVersionSettings = inputFiles.firstNotNullOfOrNull { it.languageVersionSettings }
 
             val kotlinFiles = mutableListOf<String>()
-            val jsFilesBefore = mutableListOf<String>()
-            val jsFilesAfter = mutableListOf<String>()
+            val jsFiles = mutableListOf<String>()
             val mjsFiles = mutableListOf<String>()
 
             var entryMjs: String? = "test.mjs"
@@ -80,11 +79,8 @@ abstract class BasicWasmBoxTest(
                     name.endsWith(".kt") ->
                         kotlinFiles += name
 
-                    name.endsWith("__after.js") ->
-                        jsFilesAfter += name
-
                     name.endsWith(".js") ->
-                        jsFilesBefore += name
+                        jsFiles += name
 
                     name.endsWith(".mjs") -> {
                         mjsFiles += name
@@ -98,7 +94,7 @@ abstract class BasicWasmBoxTest(
 
             val additionalJsFile = filePath.removeSuffix(".kt") + ".js"
             if (File(additionalJsFile).exists()) {
-                jsFilesBefore += additionalJsFile
+                jsFiles += additionalJsFile
             }
             val additionalMjsFile = filePath.removeSuffix(".kt") + ".mjs"
             if (File(additionalMjsFile).exists()) {
@@ -260,8 +256,7 @@ abstract class BasicWasmBoxTest(
                         }
                         vm.run(
                             "./${entryMjs}",
-                            jsFilesBefore.map { File(it).absolutePath },
-                            jsFilesAfter.map { File(it).absolutePath },
+                            jsFiles.map { File(it).absolutePath },
                             workingDirectory = dir
                         )
                         if (vm.shortName in failsIn) {

wasm/wasm.tests/test/org/jetbrains/kotlin/wasm/test/tools/WasmVM.kt

@@ -17,30 +17,28 @@ internal sealed class WasmVM(val shortName: String) {
     val name: String = javaClass.simpleName
     protected val tool = ExternalTool(System.getProperty("javascript.engine.path.$name"))
 
-    abstract fun run(entryMjs: String, jsFilesBefore: List<String>, jsFilesAfter: List<String>, workingDirectory: File?)
+    abstract fun run(entryMjs: String, jsFiles: List<String>, workingDirectory: File?)
 
     object V8 : WasmVM("V8") {
-        override fun run(entryMjs: String, jsFilesBefore: List<String>, jsFilesAfter: List<String>, workingDirectory: File?) {
+        override fun run(entryMjs: String, jsFiles: List<String>, workingDirectory: File?) {
             tool.run(
                 "--experimental-wasm-gc",
-                *jsFilesBefore.toTypedArray(),
+                *jsFiles.toTypedArray(),
                 "--module",
                 entryMjs,
-                *jsFilesAfter.toTypedArray(),
                 workingDirectory = workingDirectory
             )
         }
     }
 
     object SpiderMonkey : WasmVM("SM") {
-        override fun run(entryMjs: String, jsFilesBefore: List<String>, jsFilesAfter: List<String>, workingDirectory: File?) {
+        override fun run(entryMjs: String, jsFiles: List<String>, workingDirectory: File?) {
             tool.run(
                 "--wasm-verbose",
                 "--wasm-gc",
                 "--wasm-function-references",
-                *jsFilesBefore.flatMap { listOf("-f", it) }.toTypedArray(),
+                *jsFiles.flatMap { listOf("-f", it) }.toTypedArray(),
                 "--module=$entryMjs",
-                *jsFilesAfter.flatMap { listOf("-f", it) }.toTypedArray(),
                 workingDirectory = workingDirectory
             )
         }