Tests for obsolete KT-4798, KT-7288, KT-7046

#KT-4798 Obsolete
 #KT-7288 Obsolete
 #KT-7046 Obsolete

compiler/testData/codegen/box/intrinsics/infixCall.kt

@@ -0,0 +1,8 @@
+fun box(): String {
+    val o = "OK" charAt 0
+    val array = CharArray(2)
+    array[1] = 'K'
+    val k = array get 1
+
+    return "$o$k"
+}