Fix: support NULL input for regular expression comparison operations

[HuSen8891]

Which issue does this PR close?

Related with #11623

Rationale for this change

Regular expression comparison operations accept NULL input, like

select 'abc' ~ null;
or
select null ~ null;

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[alamb]

Thank you very much @HuSen8891 for the contribution 🙏

Can you please add some end to end tests, in sqllogicteset format?

Here are the instructions: https://github.com/apache/datafusion/tree/main/datafusion/sqllogictest

Ideally you should be able to extend one of the existing test files in https://github.com/apache/datafusion/tree/main/datafusion/sqllogictest/test_files

Perhaps https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/test_files/regexp.slt

[alamb]

I wonder if there is any reason to explicitly list out the types?

Like maybe you could simplify this a bit like

let lhs_null = matches!(lhs_type, DataType::Null);
let rhs_null = matches!(rhs_type, DataType::Null);
math (lhs_null, rhs_null) {
  (true, false) => Some(rhs_type.clone()),
  (false, true) => Some(lhs_type.clone())
  (true, true) => Some(Utf8)
  (false, false) => None,

[HuSen8891]

Here we only accept string and NULL input, not other type, such as select 'abc' ~ null;
But select 1 ~ null is not supported.

[HuSen8891]

add some end to end tests in https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/test_files/regexp.slt

[alamb]

Looks good to me -- thank you @HuSen8891

[alamb]

Thanks again @HuSen8891