[GIT-PULLS] [php-src] PR #23189: Optimize var_export

Pull Request: https://github.com/php/php-src/pull/23189
Author: kamil-tekiela

The first commit replaces `sprintf` with `memset`.

The second commit replaces `php_addcslashes` and `php_str_to_str` with a custom function based on the `smart_str_append_escaped` function from zend_smart_str.c. At one of the 3 call sites, the `php_str_to_str` was absent, and I didn't know what to do, which is why I added the flag. This makes the most sense to me, but I could also make it separate from the new function. 

I don't know whether `buffer_append_spaces` should have `inline` or not. I assume it shouldn't. 

In my simple round of testing, this proved to make `var_export` 3x faster.