scripts: csv.py: Added -l and -L shortform flags

These seem useful enough to have shortform flags:

- -l/--list-fields - Input fields before processing
- -L/--list-computed - Computed fields and expr dependencies

Note while -L/--list-computed has more information, it's also more
likely to trigger an assert/error due to poorly implemented field exprs.

scripts/csv.py

@@ -2819,11 +2819,11 @@ if __name__ == "__main__":
             action='store_true',
             help="Show what field exprs are available.")
     parser.add_argument(
-            '--list-fields',
+            '-l', '--list-fields',
             action='store_true',
             help="List fields and inferred types before processing.")
     parser.add_argument(
-            '--list-computed',
+            '-L', '--list-computed',
             action='store_true',
             help="List computed fields and expression dependencies.")
     parser.add_argument(