JVM IR: add jvmLocalClassExtractionPhase to lift out local classes from initializers

Otherwise a local class in a field initializer or anonymous init block
is copied into each constructor of the containing class (because
InitializersLowering calls deepCopy).

Since the code structure no longer resembles the original source code
here, record a custom EnclosingMethod mapping before moving such
classes, and use it in codegen.

compiler/testData/compileKotlinAgainstKotlin/metadataForMembersInLocalClassInInitializer.kt

@@ -0,0 +1,27 @@
+// TARGET_BACKEND: JVM
+// FILE: A.kt
+
+class A {
+    val o = object {
+        @JvmName("jvmGetO")
+        fun getO(): String = "O"
+    }
+
+    val k = object {
+        @get:JvmName("jvmGetK")
+        val k: String = "K"
+    }
+}
+
+// FILE: B.kt
+
+import kotlin.reflect.full.*
+
+fun box(): String {
+    val a = A()
+    val obj1 = a.o
+    val o = obj1::class.declaredMemberFunctions.single().call(obj1) as String
+    val obj2 = a.k
+    val k = obj2::class.declaredMemberProperties.single().call(obj2) as String
+    return o + k
+}