[AllOpen] Reorganize module structure of AllOpen plugin

This scheme will be common for all compiler plugins with K1 and K2 support:
- `plugin-common` contains classes shared with K1 and K2 implementations (if any)
- `plugin-k1` contains implementation for K1 compiler
- `plugin-k2` contains implementation for K2 compiler
- `plugin-backend` contains implementation for backend extensions (if any)
- `plugin-cli` is module for registration of plugin in CLI compiler
- `plugin` is a root module with tests and all submodules embedded

This structure is needed to distinguish parts related to different frontends,
  which is needed for proper dependencies settings for Kotlin IDE plugins

plugins/allopen/testData/bytecodeListing/explicitFinal.kt

@@ -0,0 +1,18 @@
+annotation class AllOpen
+
+@AllOpen
+final class Test1
+
+@AllOpen
+class Test2 {
+    fun method1() {}
+    val prop1: String = ""
+
+    final fun method2() {}
+    final val prop2: String = ""
+    final var prop3: String = ""
+
+    // Modifier 'final' is not applicable to 'setter'
+    // var prop4: String = ""
+    //     final set
+}