Distinguish script-based fresh ids with differing args

started memoizing the fresh identifiers generated by scripts to keep them
consistent across different rules. But it did not account for the script
producing a different result depending on the values of inherited
metavariables passed to it as explicit arguments.

Let’s memoize the script results in a hash map,
one fresh name per each different argument list.

Fixes: https://github.com/coccinelle/coccinelle/issues/283

Signed-off-by: Jan Tojnar <jtojnar@gmail.com>
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