Kapt: remove old JVM backend test data (2/2)

In this commit, .ir.txt expectation test data files for the JVM IR
backend are renamed to .txt. This is done as two separate commits so
that Git would recognize that these files were logically moved, not that
the contents of the original .txt files were changed.

 #KT-64680

plugins/kapt3/kapt3-compiler/testData/kotlinRunner/NestedClasses.it.txt

@@ -0,0 +1,63 @@
+package error;
+
+public final class NonExistentClass {
+}
+
+////////////////////
+
+package test;
+
+@java.lang.annotation.Retention(value = java.lang.annotation.RetentionPolicy.RUNTIME)
+@kotlin.Metadata()
+public abstract @interface MyAnnotation {
+}
+
+////////////////////
+
+package test;
+
+@kotlin.Metadata()
+public final class Simple {
+    @org.jetbrains.annotations.NotNull()
+    public static final test.Simple.Companion Companion = null;
+
+    public Simple() {
+        super();
+    }
+
+    @MyAnnotation()
+    public final void myMethod() {
+    }
+
+    @kotlin.Metadata()
+    public static final class Companion {
+
+        private Companion() {
+            super();
+        }
+    }
+
+    @kotlin.Metadata()
+    public final class InnerClass {
+
+        public InnerClass() {
+            super();
+        }
+    }
+
+    @kotlin.Metadata()
+    public static final class NestedClass {
+
+        public NestedClass() {
+            super();
+        }
+
+        @kotlin.Metadata()
+        public static final class NestedNestedClass {
+
+            public NestedNestedClass() {
+                super();
+            }
+        }
+    }
+}