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/LibDiff/Format.cpp

@@ -12,7 +12,7 @@
 namespace Diff {
 String generate_only_additions(String const& text)
 {
-    auto lines = text.split('\n', true); // Keep empty
+    auto lines = text.split('\n', SplitBehavior::KeepEmpty);
     StringBuilder builder;
     builder.appendff("@@ -0,0 +1,{} @@\n", lines.size());
     for (auto const& line : lines) {