[Test] Migrate AbstractExtendedFirDiagnosticsTest to new infrastructure

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/unused/classProperty.fir.txt

@@ -0,0 +1,15 @@
+FILE: classProperty.kt
+    public final class A : R|kotlin/Any| {
+        public constructor(): R|A| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final var v: R|kotlin/String?| = Null(null)
+            public get(): R|kotlin/String?|
+            public set(value: R|kotlin/String?|): R|kotlin/Unit|
+
+    }
+    public final fun foo(): R|kotlin/String?| {
+        lval t: R|kotlin/String?| = R|/A.A|().R|/A.v|
+        ^foo R|<local>/t|
+    }