Split ReplaceSingleLineLetInspection to SimpleRedundantLet & ComplexRedundantLet

Relates to #KT-32010

idea/testData/inspectionsLocal/complexRedundantLet/functionCallInExtension.kt

@@ -0,0 +1,7 @@
+// WITH_RUNTIME
+
+fun foo(s: String, i: Int) = s.length + i
+
+fun String.baz(): Int {
+    return let<caret> { foo(it, 1) }
+}