Don't trim list separators (#4596)

Closes #4592

Previously, we trimmed list separators, presumably under the assumption
that `#Layout` deletes all whitespace and the user may end up including
redundant whitespace. This is hacky and a faulty assumption given that
we allow custom `#Layout`.

For now, we just remove the `trim()` call. This shouldn't cause issues
downstream - I've manually checked that all `List{...}` and
`NeList{...}` declarations in the EVM, C, and WASM semantics are already
correct. If anything was missed, it's an easy fix.

A proper solution is described in #4595

Co-authored-by: rv-jenkins <[email protected]>

k-frontend/src/main/java/org/kframework/kil/UserList.java

@@ -18,13 +18,13 @@ public class UserList extends ProductionItem {
 
   public UserList(Sort sort, String separator) {
     this.sort = sort;
-    this.separator = separator.trim();
+    this.separator = separator;
     this.listType = ZERO_OR_MORE;
   }
 
   public UserList(Sort sort, String separator, String listType) {
     this.sort = sort;
-    this.separator = separator.trim();
+    this.separator = separator;
     this.listType = listType;
   }
 
@@ -58,7 +58,7 @@ public String getSeparator() {
   }
 
   public void setSeparator(String separator) {
-    this.separator = separator.trim();
+    this.separator = separator;
   }
 
   @Override