AK+Everywhere: Turn bool keep_empty to an enum in split* functions

Author: https://github.com/demostanis
Commit: 3e8b5ac920
Pull-request: https://github.com/SerenityOS/serenity/pull/15750
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/davidot
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Parser.h

@@ -192,7 +192,7 @@ public:
             // line terminators to \n is easier than splitting using all different LT characters.
             String source_string = source.replace("\r\n"sv, "\n"sv, ReplaceMode::All).replace("\r"sv, "\n"sv, ReplaceMode::All).replace(LINE_SEPARATOR_STRING, "\n"sv, ReplaceMode::All).replace(PARAGRAPH_SEPARATOR_STRING, "\n"sv, ReplaceMode::All);
             StringBuilder builder;
-            builder.append(source_string.split_view('\n', true)[position.value().line - 1]);
+            builder.append(source_string.split_view('\n', SplitBehavior::KeepEmpty)[position.value().line - 1]);
             builder.append('\n');
             for (size_t i = 0; i < position.value().column - 1; ++i)
                 builder.append(spacer);