Split ReplaceSingleLineLetInspection to SimpleRedundantLet & ComplexRedundantLet

Relates to #KT-32010

idea/testData/inspectionsLocal/complexRedundantLet/sameLets.kt

@@ -0,0 +1,12 @@
+// PROBLEM: none
+// WITH_RUNTIME
+
+
+fun foo() {
+    val foo: String? = null
+    foo?.toString()?.let<caret> {
+        it.to("")
+    }?.let {
+        it.to("")
+    }
+}