Use PointerGetDatum(cstring_to_text_with_len()) instead of CStringGetTextDatum() to avoid duplicate strlen

Hi

I found some code like the following:

> StringInfoData s;
> ...
> values[6] = CStringGetTextDatum(s.data);

The length of string can be found in ' StringInfoData.len',
but the macro CStringGetTextDatum will use strlen to count the length again.
I think we can use PointerGetDatum(cstring_to_text_with_len(s.data, s.len)) to improve.

> #define CStringGetTextDatum(s) PointerGetDatum(cstring_to_text(s))
> text *
> cstring_to_text(const char *s)
> {
> return cstring_to_text_with_len(s, strlen(s));
> }

There may have more places that can get the length of string in advance,
But that may need new variable to store it ,So I just find all StringInfoData cases.

Best regards,
houzj