Set up many basic details for Str.split- no implementation yet

compiler/module/src/low_level.rs

@@ -5,6 +5,7 @@
 pub enum LowLevel {
     StrConcat,
     StrIsEmpty,
+    StrSplit,
     ListLen,
     ListGetUnsafe,
     ListSet,

compiler/module/src/symbol.rs

@@ -660,6 +660,7 @@ define_builtins! {
         2 STR_IS_EMPTY: "isEmpty"
         3 STR_APPEND: "append"
         4 STR_CONCAT: "concat"
+        5 STR_SPLIT: "split"
     }
     4 LIST: "List" => {
         0 LIST_LIST: "List" imported // the List.List type alias