Added BBF hook to adjust 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 adjusted(truncated/rounded) to the correct scale. To get this behaviour added hooks at following places to adjust the result value.

• evaluate_expr() - All the arithmetic computations that result in constant value, happens here. So added a hook to adjust the result after every such arithmetic computation.
• ExecInterpExpr() - All the arithmetic computations other than mentioned above, happens here. So added a hook to adjust the result after every such arithmetic computation.
• finalize_aggregate() - For aggregate functions, the final result is computed here, so added a hook to adjust 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.
• added pltsql_exprTypmod_hook to compute expression typmod for expressions whose typmod is not computed by exprTypmod.
• During initialisation of resulttype in function ExecInitResultTypeTL added hook ExecUpdateResultTypeTL_hook to set correct typmod of all attributes of result tuple.

Extension PR: babelfish-for-postgresql/babelfish_extensions#3455

Issues Resolved

BABEL-5467

Check List

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[shah-nirmit]

Question: For every FuncExpr we will enter this hook, extra instructions for every expression evaluation, seems to me it will affect performance