Improve lpad udf by using a GenericStringBuilder

[Omega359]

Is your feature request related to a problem or challenge?

As noted in the discussion in #11941 (comment) it looks like the performance of the lpad udf may be improved a bit by using a GenericStringBuilder instead of creating a string every time.

As well, as noted in #11941 (comment) there may be room for improvement with the general code.

Describe the solution you'd like

lpad udf updated to use a GenericStringBuilder and a benchmark added to showcase whether it improves performance or not

Describe alternatives you've considered

No response

Additional context

No response

[Omega359]

take