Add inspection to simplify successive null checks #KT-14799 Fixed

idea/testData/inspectionsLocal/nullChecksToSafeCall/unstableExtensionInChain.kt

@@ -0,0 +1,12 @@
+// PROBLEM: none
+val a: Testtt? = Testtt()
+
+fun main(args: Array<String>) {
+    if (a<caret> != null && a.a != null) {
+
+    }
+}
+
+class Testtt
+
+val Testtt?.a: Testtt? get() = null