Fix #81407: shmop_open won't attach and causes php to crash

We need to allocate buffers for the file mapping names which are large
enough for all potential keys (`key_t` is defined as `i

Fix #81407: shmop_open won't attach and causes php to crash

We need to allocate buffers for the file mapping names which are large
enough for all potential keys (`key_t` is defined as `int` on Windows).

Regarding the test: it's probably never a good idea to use hard-coded
keys (should always use `ftok()` instead), but to reliably reproduce
this Windows specific issue we need to, and it shouldn't be an issue on
that OS.

Closes GH-7448.

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