Added BBF hook to truncate numeric result to correct scale

[rohit01010]

Description

For Babelfish, the expected behaviour should be for every arithmetic computation which results in numeric datatype, the result should be truncated to the correct scale. To get this behaviour added hooks at following places to truncate the result value.

• evaluate_expr() - All the arithmetic computations that result in constant value, happens here. So added a hook to truncate the result after every such arithmetic computation.
• ExecInterpExpr() - All the arithmetic computations other than mentioned above, happens here. So added a hook to truncate the result after every such arithmetic computation.
• finalize_aggregate() - For aggregate functions, the final result is computed here, so added a hook to truncate the result for aggregate functions.

Also, for some nodes such as T_OpExpr, T_DistinctExpr, T_CoerceViaIO the result_typmod was directly hardcoded as -1 in PostgreSQL, Added hook pltsql_exprTypmod_hook to compute the typmod of the expression and passed those instead of -1 to avoid losing typmod information. Also, added pltsql_exprTypmod_hook to compute expression typmod for expressions whose typmod is not computed by exprTypmod.

Extension PR: babelfish-for-postgresql/babelfish_extensions#3521
Cherry-picked from: #529

Issues Resolved

BABEL-5467

Check List

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