Fix bug #73182: PHP SOAPClient does not support stream context HTTP headers in array form

This code is modelled after how `http_fopen_wrapper.c` does things,
which apparently is just loo

Fix bug #73182: PHP SOAPClient does not support stream context HTTP headers in array form

This code is modelled after how `http_fopen_wrapper.c` does things,
which apparently is just looping over the array and handling each string
the same way as if we passed a header string directly.

Also fixes a potential crash in `php_sdl.c` but without adding support
for header arrays there (yet) because the code is untested.

Closes GH-15817.

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