handle 0 and NULL value of NTH_VALUE function

[thinh2]

Which issue does this PR close?

Closes #12320.

Rationale for this change

The root cause in #12320 is because get_signed_integer_value will return an error on NULL or Int64(NULL) value. To process the nth_value function, it requires the n value should be an integer. Therefore, I decided to convert NULL value to 0 in get_signed_integer_value and implement handler for the 0 case. This will evaluate to NULL value for the nth_value(v1, NULL) expression.

Furthermore, it also evaluate the nth_value(v1, 0) to NULL instead of generating panic, which match the expected behaviour in duckdb.

What changes are included in this PR?

[x] Return 0 for NULL value in get_signed_integer
[x] Handle nth_value execution when n is 0
[x] Test file updated to test nth_value(v2, 0), nth_value(v2, NULL) and nth_value(v2, v2 * NULL).

Are these changes tested?

Yes

Are there any user-facing changes?

[jayzhan211]

👍