Fix: pgrx cannot find function after numeric change interface

[jiaqizho]

Change logs

After CBDB public part of numeric defines, then numeric_is_nan/numeric_is_inf have been replace with macro NUMERIC_IS_NAN/NUMERIC_IS_INF.

But some of extension may not write by c/c++, then it can't direct call the macro NUMERIC_IS_NAN/NUMERIC_IS_INF. So current change add these function back.

Why are the changes needed?

nope

Does this PR introduce any user-facing change?

nope

How was this patch tested?

nope

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[my-ship-it]

LGTM

[jiaqizho]

@my-ship-it merge please