Replace UastConverter with UastLanguagePlugin, allow additional checkers

plugins/uast-common/src/org/jetbrains/uast/UastContext.kt

@@ -16,15 +16,15 @@
 package org.jetbrains.uast
 
 interface UastContext {
-    val converters: List<UastConverter>
+    val languagePlugins: List<UastLanguagePlugin>
 
     fun convert(element: Any?): UElement? {
         if (element == null) {
             return null
         }
 
-        for (converter in converters) {
-            val uelement = converter.convertWithParent(element)
+        for (plugin in languagePlugins) {
+            val uelement = plugin.converter.convertWithParent(element)
             if (uelement != null) {
                 return uelement
             }

plugins/uast-common/src/org/jetbrains/uast/UastLanguagePlugin.kt

@@ -22,9 +22,18 @@ interface UastConverter {
     fun isFileSupported(path: String): Boolean
 }
 
+interface UastLanguagePlugin {
+    val converter: UastConverter
+    val additionalCheckers: List<UastAdditionalChecker>
+}
+
+interface UastAdditionalChecker {
+    operator fun invoke(element: UElement, handler: UastHandler, context: UastContext)
+}
+
 object UastConverterUtils {
     @JvmStatic
-    fun isFileSupported(converters: List<UastConverter>, path: String): Boolean {
-        return converters.any { it.isFileSupported(path) }
+    fun isFileSupported(converters: List<UastLanguagePlugin>, path: String): Boolean {
+        return converters.any { it.converter.isFileSupported(path) }
     }
 }