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

As discussed on GH-5632, the HTML functionality does not appear
to be in active use. For HTML rendering of test results, it is
suggested to instead use the JUnit integration, in combination
with your favorite JUnit viewer.

Closes GH-5705.

Don't connect to each worker individually: First spawn all processes
and then establish connections in any order.

This avoids a ~1s wait when running on many cores.

The test runner currently defaults to running the entire test suite if
no selected tests can be found. This can be unexpected.

For example the ext/mysqlnd/ directory has no tests, if you specify that
directory when testing the entire test suite will be run.

    run-tests.php [options] ext/mysqlnd/

Closes GH-5605.

--file-cache-prime populates the file cache,
--file-cache-use uses the file cache.

And fix a number of tests to run under file cache or disabled
timestamp validation.