[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/nestedInner.txt

@@ -0,0 +1,32 @@
+@java.lang.annotation.Retention(value=RUNTIME)
+@kotlin.Metadata
+public annotation class AllOpen {
+    // source: 'nestedInner.kt'
+}
+
+@kotlin.Metadata
+public final class Test$Inner {
+    // source: 'nestedInner.kt'
+    synthetic final field this$0: Test
+    public method <init>(p0: Test): void
+    public final method innerMethod(): void
+    public final inner class Test$Inner
+}
+
+@kotlin.Metadata
+public final class Test$Nested {
+    // source: 'nestedInner.kt'
+    public method <init>(): void
+    public final method nestedMethod(): void
+    public final inner class Test$Nested
+}
+
+@AllOpen
+@kotlin.Metadata
+public class Test {
+    // source: 'nestedInner.kt'
+    public method <init>(): void
+    public method testMethod(): void
+    public final inner class Test$Inner
+    public final inner class Test$Nested
+}