KT-5347 VerifyError on local data class with closure

- generated copy() should push captured fields on stack
- refactor context lookup
- handle vars in local classes using instance fields

 #KT-5347 Fixed

compiler/testData/codegen/box/classes/kt5347.kt

@@ -0,0 +1,44 @@
+fun test1(str: String): String {
+    @data class A(val x: Int) {
+        fun foo() = str
+    }
+    return A(0).copy().foo()
+}
+
+class TestClass(val x: String) {
+    fun foo(): String {
+        @data class A(val x: Int) {
+            fun foo() = this@TestClass.x
+        }
+        return A(0).copy().foo()
+    }
+}
+
+fun test2(str: String): String = TestClass(str).foo()
+
+fun test3(str: String): String {
+    var xx = ""
+    @data class A(val x: Int) {
+        fun foo(): String { xx = str; return xx }
+    }
+    return A(0).copy().foo()
+}
+
+fun test4(str: String): String {
+    var xx = ""
+    fun bar(s: String): String { xx = s; return xx }
+    @data class A(val x: Int) {
+        fun foo(): String = bar(str)
+    }
+    return A(0).copy().foo()
+}
+
+fun box(): String {
+    return when {
+        test1("test1") != "test1" -> "Failed #1 (parameter capture)"
+        test2("test2") != "test2" -> "Failed #2 ('this' capture)"
+        test3("test3") != "test3" -> "Failed #3 ('var' capture)"
+        test4("test4") != "test4" -> "Failed #4 (local function capture)"
+        else -> "OK"
+    }
+}