feat:implement sql style 'find_in_set' string function

[Syleechan]

Which issue does this PR close?

https://dev.mysql.com/doc/refman/8.0/en/string-functions.html#function_find-in-set:~:text=FIND_IN_SET(str%2Cstrlist)

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[alamb]

Thank you for the contribution @Syleechan -- this PR seems pretty mysql specific and maybe it belong in a downstream system given:

1. There is already a function like array_contains
2. DataFusion isn't trying to replicate the full function library of existing databases

[alamb]

What do you think about using one of the existing array union functions instead? What about array_contains?

[Syleechan]

Thanks @alamb . I have checked that the array functions input args type are different from the string function find_in_set.Actually, we use calcite to transfer to datafusion to compute data, and calcite also has array_contains, array_position functions.But Calcite take them as different functions, array functions process array input args and string functions process string input args.
https://calcite.apache.org/docs/reference.html#:~:text=ARRAY_POSITION(array%2C%20element)
https://calcite.apache.org/docs/reference.html#:~:text=FIND_IN_SET(matchStr%2C%20textStr)
these are calcite style functions in the reference.

[Ted-Jiang]

LGTM, thx @Syleechan. @alamb this is the last str_func user case in our system, but we want to introduce more array_func, @Syleechan could you plz help list the need list.

[alamb]

Thanks again @Syleechan