JVM_IR: KT-40330 Unify field names for captured 'this' with JVM

NB some cases such as captured extension receiver for an extension
lambda are not supported yet; to be discussed, to what extent should we
actually follow JVM code shape here.

compiler/testData/codegen/bytecodeText/fieldsForCapturedValues/extensionReceiver.kt

@@ -0,0 +1,17 @@
+class Receiver {
+    fun foo() {}
+}
+
+fun Receiver.bar() {
+    class NamedLocal {
+        fun run() {
+            foo()
+        }
+    }
+}
+
+// JVM_TEMPLATES
+// 1 final synthetic LReceiver; \$this_bar
+
+// JVM_IR_TEMPLATES
+// 1 private final synthetic LReceiver; \$this_bar