Update the design of parameter helpers

[SLMT]

This PR updates the design of parameter helpers so that we can use the helpers in both JDBC and stored procedures. Before merging this PR, the reviewers must first ensure that the corresponding changes in VanillaCore is merged.

Here are the major changes in this PR:

• A parameter helper is now separated into two classes. One is for dealing with unpacking parameters, and another is for dealing with the result sets of stored procedures. The later one extends the former one in order to reuse the code. Now we call the former one a parameter helper and the later one a stored procedure helper (SpHelper).
• All parameter helpers are now put in org.vanilladb.bench.benchmarks.xxx.rte packages
• All sp helpers are now put in org.vanilladb.bench.server.procedure.xxx packages
• All variables are renamed to reflect the above changes.