Add a `zend.exception_string_param_max_len` ini setting.
(same suffix as `log_errors_max_len`)
Allow values between 0 and 1000000 bytes.
For example, with zend.exception_string_param_max_len=0,
"" would represent the empty string, and "..." would represent something
longer than the empty string.
Previously, this was hardcoded as exactly 15 bytes.
Discussion: https://externals.io/message/110717
Closes GH-5769
07db64156e