Feature: extend int128 to numeric interface

[jiaqizho]

fix #ISSUE_Number

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Change logs

CBDB not allow building pg numeric from other formats. Numeric objects can only be constructed from string, which means that the caller needs to convert its own data into a specific format string, then convert the string into numeric. This is a very inefficient method.

Current change provider a new method int128_to_numeric which used to build a numeric from int128. Also, current method allow build special numeric or build numeric with scale.

Why are the changes needed?

Allow caller build numeric from int128

Does this PR introduce any user-facing change?

nope

How was this patch tested?

ci

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[my-ship-it]

No need to change in numeric.c?

[jiaqizho]

after #392 , no need current change any more.