[FIR] Unify some special names to make code more uniform

core/compiler.common/src/org/jetbrains/kotlin/name/SpecialNames.kt

@@ -61,6 +61,24 @@ object SpecialNames {
     @JvmField
     val IMPLICIT_SET_PARAMETER = Name.special("<set-?>")
 
+    @JvmField
+    val ARRAY = Name.special("<array>")
+
+    @JvmField
+    val RECEIVER = Name.special("<receiver>")
+
+    /**
+     * Special name to store expressions used as indexes in subscription operators (`get` and `set`).
+     *
+     * For example, `bar1()` and `bar2()` are indexes in `foo[bar1(), bar2()]` call.
+     */
+    @JvmStatic
+    fun subscribeOperatorIndex(idx: Int): Name {
+        require(idx >= 0) { "Index should be non-negative, but was $idx" }
+
+        return Name.special("<index_$idx>")
+    }
+
     @JvmStatic
     fun safeIdentifier(name: Name?): Name {
         return if (name != null && !name.isSpecial) name else SAFE_IDENTIFIER_FOR_NO_NAME