JVM: rename this$0 when regenerating nested objects too

In the old backend, this was unnecessary because nested objects would
reference their lambdas' captures through the original this$0. On
JVM_IR, using loose capture fields means a name/descriptor clash can
occur on any level of nesting, not just the top.

compiler/testData/codegen/boxInline/anonymousObject/twoCapturedReceivers/kt8668_nested.kt

@@ -0,0 +1,14 @@
+// FILE: 1.kt
+package test
+
+class C(val x: String) {
+    fun f(y: String) = C(y).g { x }
+
+    inline fun g(crossinline h: () -> String) =
+        { { h() + x }() }()
+}
+
+// FILE: 2.kt
+import test.*
+
+fun box() = C("O").f("K")

compiler/testData/codegen/boxInline/anonymousObject/twoCapturedReceivers/kt8668_nested_2.kt

@@ -0,0 +1,14 @@
+// FILE: 1.kt
+package test
+
+class C(val x: String) {
+    inline fun f(crossinline h: () -> String) = C("").g { x + h() }
+
+    inline fun g(crossinline h: () -> String) =
+        { { h() + x }() }()
+}
+
+// FILE: 2.kt
+import test.*
+
+fun box() = C("O").f { "K" }