What problem does this PR solve?

Issue Number: close #64681

Problem Summary:

NumericArithmetic.divideDecimal (the DECIMALV2 constant-folding divide function) guarded against division by zero by checking the numerator (first) instead of the denominator (second):

public static Expression divideDecimal(DecimalLiteral first, DecimalLiteral second) {
    if (first.getValue().compareTo(BigDecimal.ZERO) == 0) {   // wrong operand
        return new NullLiteral(first.getDataType());
    }
    BigDecimal result = first.getValue().divide(second.getValue());
    return new DecimalLiteral(result);
}

As a result, when both operands are DECIMALV2 literals:

• 0 / x folded to NULL instead of 0 — a silent wrong result.
• x / 0 skipped the guard and called BigDecimal.divide(ZERO), throwing ArithmeticException. This is caught by ExpressionEvaluator.invoke and the expression is left unfolded (BE then evaluates it and returns NULL), so it is not a crash, but the FE folding path is incorrect.

The sibling functions divideDouble and divideDecimalV3 both correctly check second. This PR aligns divideDecimal with them by checking the denominator. Division by zero continues to return NULL, matching Doris/MySQL semantics (Doris is MySQL-compatible here; it does not raise the ANSI division by zero error).

Release note

Fix incorrect constant folding of DECIMALV2 division: 0 / x was folded to NULL instead of 0.

Check List (For Author)

• Test

  • Unit Test (added testDivideDecimalZeroNumerator and testDivideDecimalZeroDenominator in NumericArithmeticTest)

• Behavior changed:

  • Yes. 0 / x over constant DECIMALV2 values now correctly folds to 0 instead of NULL. Division by zero still returns NULL (unchanged).

• Does this need documentation?

  • No.