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/multipleExtensionReceivers.kt

@@ -0,0 +1,26 @@
+class Foo {
+    fun foo() {}
+}
+
+class Bar {
+    fun bar() {}
+}
+
+fun Foo.test(bar: Bar) {
+    fun Bar.test() {
+        class Local {
+            fun run() {
+                foo()
+                bar()
+            }
+        }
+    }
+}
+
+// JVM_TEMPLATES
+// 1 final synthetic LMultipleExtensionReceiversKt\$test\$1; this\$0
+// 1 final synthetic LBar; \$this_test
+
+// JVM_IR_TEMPLATES
+// 1 private final synthetic LFoo; \$this_test
+// 1 private final synthetic LBar; \$this_test\$1