Fix: pgrx cannot find function after numeric change interface (#410)

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.

src/backend/utils/adt/numeric.c

@@ -546,6 +546,51 @@ numeric_is_integral(Numeric num)
 	return (arg.ndigits == 0 || arg.ndigits <= arg.weight + 1);
 }
 
+
+/*
+ * numeric_is_nan() -
+ *
+ *	Is Numeric value a NaN?
+ */
+bool
+numeric_is_nan(Numeric num)
+{
+	return NUMERIC_IS_NAN(num);
+}
+
+/*
+ * numeric_digits() -
+ *
+ *	Output function for numeric's digits
+ */
+NumericDigit *
+numeric_digits(Numeric num)
+{
+	return NUMERIC_DIGITS(num);
+}
+
+/*
+ * numeric_len() -
+ *
+ *	Output size of digits in bytes
+ */
+int
+numeric_len(Numeric num)
+{
+	return NUMERIC_NDIGITS(num) * sizeof(NumericDigit);
+}
+
+/*
+ * numeric_is_inf() -
+ *
+ *	Is Numeric value an infinity?
+ */
+bool
+numeric_is_inf(Numeric num)
+{
+	return NUMERIC_IS_INF(num);
+}
+
 /*
  * numeric_maximum_size() -
  *

src/include/utils/numeric.h

@@ -342,6 +342,16 @@ extern float8 numeric_li_fraction(Numeric x, Numeric x0, Numeric x1,
 								  bool *eq_bounds, bool *eq_abscissas);
 extern Numeric numeric_li_value(float8 f, Numeric y0, Numeric y1);
 
+/*
+ * Some of utility functions. which have same definition as the macro,
+ * but some of extension will these function rather than use the marco
+ * like `pgrx`.
+ */
+extern int16 *numeric_digits(Numeric num);
+extern int numeric_len(Numeric num);
+extern bool numeric_is_nan(Numeric num);
+extern bool numeric_is_inf(Numeric num);
+
 /*
  * Utility functions in numeric.c
  */